DEPARTMENT OF COMMERCE

TECHNOLOGIC PAPERS

OP THE

BUREAU OF STANDARDS

S. W. STRATTON. DIRECTOR

No. 2O2

RESULTS OF

A SURVEY OF ELEVATOR INTERLOCKS

AND AN ANALYSIS OF ELEVATOR

ACCIDENT STATISTICS

C. E. OAKES, Electrical Engineer

J. A. DICKINSON, Mechanical Engineer

Bureau of Standards
OCTOBER 17, 1921

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Sold only by the Superintendent of Documents, Government Printing Office
Washington, D. C.

WASHINGTON

GOVERNMENT PRINTING OFFICE
1921

DEPARTMENT OF COMMERCE

TECHNOLOGIC PAPERS

OF THE

BUREAU OF STANDARDS

S. W. STRATTON. DIRECTOR

No. 2O2

RESULTS OF

A SURVEY OF ELEVATOR INTERLOCKS

AND AN ANALYSIS OF ELEVATOR

ACCIDENT STATISTICS

C. E. OAKES, Electrical Engineer

J. A. DICKINSON, Mechanical Engineer

Bureau of Standards

OCTOBER 17, 1921

PRICE. 5 CENTS

Sold only by the Superintendent of Documents, Government Printing Office
Washington. D. C.

WASHINGTON
GOVERNMENT PRINTING OFFICE

1921

RESULTS OF A SURVEY OF ELEVATOR INTERLOCKS

AND AN ANALYSIS OF ELEVATOR ACCIDENT

STATISTICS

By C. E. Oakes and J. A. Dickinson

ABSTRACT

This report gives the results of a field survey of several thousand elevator landings
equipped with various types of mechanical and electromechanical interlocks and
contact devices. The survey was conducted in connection with the preparation of
an elevator safety code, in which work the Bureau of Standards engineers have co-
operated with engineers of the American Society of Mechanical Engineers. The
elevators are classified: A, Elevators in buildings having heavy service and where
maintenance service is provided; B, elevators located in buildings where the service
is heavy but without maintenance; and C, elevators on which the service is light and
for which no maintenance service is provided. The statistics show that 73.8 per cent
of all fatal accidents might be prevented by well-designed interlocks.

CONTENTS

Page

I. Introduction 3

II. Report on a field survey of elevator interlocks and contacts 4

1. Hoistway-door protective devices 5

2. Emergency release g

3. Field survey 9

4. Division of buildings into classes according to conditions of service

and maintenance 9

5. Discussion of conditions under which devices must operate 10

6. Tabulation of results of survey n

7. Discussion of survey 15

III. Summary of advantages and disadvantages of various types of devices. . . 18

IV. Elevator-accident statistics 21

r. Group I. General: Reports of accidents received through clipping

bureaus 21

2. Group II. Reports from State industrial commissions 22

3. Group III. Municipal statistics 25

V. Suggested requirements to be included in an elevator code 28

1. Definitions 28

2. Specifications 29

I. INTRODUCTION

During the European War the Bureau of Standards cooperated
with the Federal safety engineers in preparing elevator rules,
intended primarily for the use of Government navy yards, arse-

4 Technologic Papers of the Bureau of Standards

nals, and explosive plants. The code was based on existing regu-
lations as prepared by various States and municipalities, together
with suggestions from elevator manufacturers and safety engineers.
This work was completed in the spring of 1918. Following the
completion of this code the Bureau was requested to revise the
Federal code to render it suitable for general application.

The American Society of Mechanical Engineers published an
elevator code in 1917, which was prepared by the subcommittee
on the protection of industrial workers. A complete revision of
this code was undertaken a few months after its publication. In
order to avoid duplication of effort, the Bureau in 1918, at the
invitation of the American Society of Mechanical Engineers, began
to cooperate in the further development of this code. The Bureau
placed the data it had collected at the disposal of the American
Society of Mechanical Engineers' committee and later, in 1919,
abandoned all idea of separate development and publication of an
elevator safety code, but continued to cooperate with the A. S.
M. E. committee with the idea of developing a single national
code.

Early in the work it became evident that the point of greatest
controversy was the question of proper hoistway-door protection.
The Bureau of Standards decided to make a field survey of the
various types of interlocks and contacts in use and did so in 1918
and 1919. The results were submitted to the committee for its
use in drafting the portion of the code dealing with such devices.

This paper gives the final results of the survey and a collection
of statistics from other sources which have been classified and
arranged to show the relation of accidents to hoistway-door pro-
tection.

U. REPORT ON A FIELD SURVEY OF ELEVATOR INTER-
LOCKS AND CONTACTS

In the preparation of a safety code of any kind the need for
reliable data upon which to base the various requirements is self-
evident.

There are certain hazards which are obviously apparent. It
may be, however, that hazards of a far graver nature exist which
are not apparent to a person making a casual survey of the in-
dustry. Ofttimes these less apparent hazards prove to be more
serious than those readily apparent. A careful study of acci-
dent statistics taken from as large a number of sources as possi-

Elevator Interlock Report 5

ble will indicate in a general way the particular parts or types of
machines responsible for the more serious accidents.

A summary of the accidents given in the appended tables will
show that by far the larger portion of elevator accidents occur
at the hoistway door. The question, therefore, of the best method
of reducing this hazard is one to which considerable study has
been given.

1. HOISTWAY-DOOR PROTECTIVE DEVICES

All forms of hoistway-door protective devices may be broadly
classified in three divisions, according to the method of locking
the car and the hoistway door.

THE MECHANICAL TYPE. This type of door safety depends
on mechanical action to lock the car-control mechanism while the
door is open and to hold the door in the locked position when the
car is not at the landing. The functions of this device are gener-
ally as follows : (a) Release of hoistway door, (b) locking control
mechanism, (c) release of control mechanism, and (d) locking of
hoistway door.

In most types the locking of the hoistway door is accomplished
by holding locked, either by means of a very substantial latch or
a properly shaped slot in a rotating member, a bar fastened
rigidly to the hoistway door. Generally, the door-locking mecha-
nism is substantial in construction and will stand a large amount
of wear without loss of function. Mechanisms which do not
depend entirely on spring action to hold the door locked are
preferable.

The methods of interlocking the car and door are varied. A
variety of methods are necessary, owing to the large number of
different types of control mechanism used on different makes and
types of elevators. Two popular styles in use are (a) a slotted
flap which upon the opening of the landing door drops from a
vertical to a horizontal position, the slot engaging and holding
inoperative the car-control lever in the neutral position; (6) a
device in which an arc of a circle properly slotted is fastened to
the control lever. A bolt or rod engages in this slot, thus pre-
venting the motion of the operating lever when the lever is in
the neutral position and the car door open. As a rule these
devices are satisfactory. Occasionally, however, installations are
found in which there is too much lost motion, and in certain
hydraulic installations it is possible to start the car very slowly,
due to the slight motion allowed on the control lever when the

6 Technologic Papers of the Bureau of Standards

car is in the "locked" position. This objection does not ordi-
narily hold true in case of electrically controlled elevators, as the
operating lever must move through an appreciable arc before the
operating circuit is completed, although in controllers with a
number of contact steps the first contact may be so close to the
' ' stop ' ' position that cases have been noted in which the car may
be moved slowly with the interlocking mechanism in the ' ' locked ' '
position. As installed at the present time, a great many of these
devices have accessible metal parts in the car, the removal or
blocking of which may render the device inoperative. Such parts
as are located within the car should be inclosed.

One of the features generally incorporated in this type of lock
is some form of limiting device which will prevent the opening
of the hoistway door except when the car is within 3 or 4 inches
of the landing at which the stop is to be made.

The inclusion of a landing range in an interlock device is not a
necessary adjunct to the interlocking function. It is a mechanical
detail which is inherent in certain types of devices where inter-
locking is secured by mechanical means. The absence of a
landing range detracts in no way from the proper functioning of
a well-designed interlock. The use of a device of this kind is
intended to lessen the number of accidents due to persons trip-
ping on entering or leaving the car. Such accidents are, however,
relatively unimportant, the minor nature of these accidents being
emphasized by the fact that statistics concerning them are not
generally recorded separately.

At the request of the Bureau of Standards a list of tripping
accidents was prepared by one of the largest casualty insurance
companies, the list including all tripping accidents occurring on
elevators insured by them during the year 1919. An analysis of
this list shows that more tripping accidents occurred when the
car platform was within 3 inches of the landing level than occurred
when the car platform was more than 3 inches away. In other
words, a 3 -inch stopping range would not have prevented the
majority of these accidents. The consideration of a more or less
parallel case may be of interest: A person frequently trips over
a projection in a sidewalk where the difference of elevation is
slight, but almost never trips over a curbstone where the differ-
ence of elevation is considerable. It appears that threshold
illumination is an important consideration in preventing tripping
accidents and should be given careful attention, if such accidents
are to be avoided.

Elevator Interlock Report 7

Leveling devices, both automatic and manually controlled, are
now on the market and can be used on either passenger or freight
elevators. These devices bring the car flush with the landing, and
in the case of the automatic device maintain it there during loading
and unloading and are doubtless the most effective devices avail-
able for decreasing accidents from tripping.

ELECTROMECHANICAL. The second broad division into which
door safety devices may be placed is the electromechanical type,
in which the door is mechanically held closed but in which the car
is interlocked by means of some form of electrical control. This
may be accomplished either by interrupting the master or control
circuit or by running an independent circuit which will interrupt
the operating current on the machine control board or, in the case
of hydraulic installations, by using a current to actuate a solenoid
which in turn mechanically locks the car-control lever or holds
closed a valve in the supply line, thus preventing motion of the car.

This type of device (electromechanical) may or may not limit
the stopping of a car to within a few inches of the landing plat-
form before the door can be opened. Those devices in which
the electric contact is place^.jm^i:jthe_car_must necessarily be
provided with a stopping range limit, and their operation pre-
vents the opening of jthe hoistway door unless the car is within
a predetermined distance of the landing flooFTevel, while those
depending' on switches placed in the hoistway~can generally be
opened without respect to the relative position of the car and
hoistway landing platform.

The door-locking mechanisms used in devices of this kind are
varied. Those with the undercar contact generally use the same
mechanism as is employed in the purely mechanical type, while
those with a hoistway contact generally make use of a bar-lock or
some form of toggle-joint device. Of the two the latter is prefer-
able, as it does not depend on springs to hold the door locked.

ELECTRIC CONTACT DEVICES. The third class of door safety
devices comprises a wide variety of electric hoistway-door con-
tacts. These devices are generally connected in series known as
shaft-series system and operate on the car-control circuit, although
they may be wired so that each door is a separate unit, this wiring
being known as a door-unit system. Those in which the switch
is actuated by the door itself (there are a large variety of this
type) give considerable trouble, due to lack of alignment of the
door and switch and to vibration and the impact of the door.

8 Technologic Papers of the Bureau of Standards

The difference between a hoistway-door contact and an electro-
mechanical interlock should be clearly kept in mind. A contact
device holds the car inoperative when the door opposite which
the car is standing is open. An electromechanical interlock is a
device which holds the car inoperative when the door opposite
which the car is standing is open or unlocked and in addition
holds locked the hoistway door when the car is not at the landing.
This door-locking function is accomplished by a mechanism inde-
pendent of, and separate from, the ordinary door latch.

In other words, a contact is a device which can only prevent the
motion of the car when a door is open. It can not and does not
hold locked the door when the car is not at the landing. The
ordinary hoistway-door latch must be used as the door-locking
device.

The electromechanical device has a bar or other form of lock
incorporated in it and so arranged and interconnected that the
door must be closed and locked before the car can be started.

In order to obtain information regarding the effectiveness of
the ordinary hoistway-door latch, a survey was made of several
hundred hoistway doors. The results of this survey indicate
that 30 per cent of the latches were out of order, the principal
causes of failure being worn latch parts, worn door hangers,
loosening of latch from door, and lack of lubrication. Many
latches were so poorly designed that if the door were closed
quickly the rebound of the door would occur before the latch
engaged. An analysis of elevator-accident statistics shows that
about one-third of the accidents occur by persons falling down
the shaft. This is in itself an indication that the ordinary latch
is unreliable and shows why a contact device can not of itself
offer complete hoistway-door protection. In the other two types
of device (mechanical and electromechanical) the door is held
shut mechanically whether or not the car interlocking feature is

working.

2. EMERGENCY RELEASE

Every elevator car equipped with interlocks should be provided
with an emergency switch or release device located in the car. If
there is a fire, panic, or other emergency, or if the car becomes
stalled in the shaft due to failure of the door safety circuit, the
operation of the emergency device will permit the elevator to con-
tinue in operation. Unless this device is properly designed and
installed its use may be subject to much abuse.

Elevator Interlock Report 9

An undesirable feature of an emergency switch so designed
that the switch can be turned "on" or "off" is that, in event of
failure of any contact, the throwing of an emergency switch leaves
the entire system with no protection other than that offered by
the ordinary door latch, which is notoriously unreliable. The
emergency release generally consists of a two-pole push or snap
switch sometimes placed in a case under a glass cover, often
without even this protection, and when once thrown is quite
likely to be left in the "emergency" position for weeks or months.
Except where required by law, the spring-type switch, which
must be held in the emergency position by the operator, is seldom
seen, although it is obviously the most desirable type. The
emergency-release device for mechanical locks which remains in
the emergency-operating position without being held there by
the operator is equally undesirable.

3. FIELD SURVEY

In order to obtain reliable information regarding door protective
devices, a large number of passenger elevators were inspected
by representatives of the Bureau of Standards and thousands of
doorways and landings examined. These inspections covered a
considerable range of territory, and territories in which the legal
requirements for the protection of entrance doors to elevators
differ widely. The following statement gives the various cities
and States in which data were secured and the legal requirements
in each place :

Requirements

Philadelphia Mechanical or electromechanical interlocks of the undercar

contact type.
Pennsylvania (outside of
cities of first or second

class) Mechanical or electromechanical interlocks and car-door

contacts on cars driven by electricity.

New Jersey Mechanical or electromechanical.

New York City No interlock requirements.

4. DIVISION OF BUILDINGS INTO CLASSES ACCORDING TO CONDITIONS
OF SERVICE AND MAINTENANCE

For the convenience in analyzing the performance under actual
operating conditions of any given interlock device or group of
such devices it is desirable to divide the elevators which they
protect into three general classes, the classification being natu-
rally somewhat elastic. The two factors which govern this classi-

61693 21 2

io Technologic Papers of tlie Bureau of Standards

fication are the amount of duty rendered and the maintenance
service they receive. The grouping adopted is as follows:

CLASS A. Those in which the volume of travel is heavy and for
which there is a special elevator maintenance and inspection
service. Into this class will fall: (a) Large office buildings, (6)
first-class hotels, (c) high-grade apartment houses, (d) large rail-
road terminals, (e) municipal and State buildings in cities, and
(/) large department stores. This class is generally limited to the
larger cities.

CLASS B. Buildings in which the travel is heavy, but in which
no regular maintenance or inspection service is provided. In
this are included the following types of buildings: (a) Small
office buildings in large cities, (6) large office buildings in small
cities, (c) loft and manufacturing buildings, (d) small hotels in
cities, (e) medium-size apartment houses, (/) small department
stores in cities, and (g) other retail stores in cities.

CLASS C. Buildings that have light service and receive but
little care and attention. In this class will fall: (a) Small office
buildings in towns or small cities, (b) storage or warehouse build-
ings, (c) small hotels, (d) manufacturing plants where the upper
floors are used largely for storage, and (e) very small shops and
retail stores (such as furniture stores) where most of the selling
is done on the ground floor.

5. DISCUSSION OF CONDITIONS UNDER WHICH DEVICES MUST

OPERATE

In Class A buildings the vital consideration is speed of service.
In most installations of this class there are several load peaks, and
at such times every car is run at capacity. A loss of a half minute
a trip per elevator would mean a serious curtailment of service.
Any device that is installed must not reduce the operating speed
to any marked degree. Further, it must be provided with some
form of emergency release, so that the failure of the device or of
any part of it will not tie up the car during the rush period.

The survey showed that there is generally very little operating
trouble due to failure of door-safety equipment in Class A build-
ings, because ample maintenance service is provided. As a rule,
the elevator maintenance crew take pride in the condition of the
equipment under its care and keep parts properly adjusted and in
repair.

In Class B buildings the vital consideration is simplicity and
ruggedness, as the service in this class of buildings is severe and

Elevator Interlock Report 1 1

the maintenance and attention which elevator parts and devices
will receive is slight. Lack of alignment on the part of the
elevator or of the hoistway door may cause excessive wear of the
interlock or contact, causing rapid deterioration, which results
ultimately in failure to operate.

As a usual thing the only attention which a Class B elevator
receives is an occasional "going over" by some mechanic or handy
man for the purpose of lubrication. Even this perfunctory oiling
is done at odd times and at very irregular intervals. It is very
seldom that the elevators in a Class B building are in charge of a
starter, and it is only in very exceptional cases that the operators
are given any definite instructions as to the operation of the car;
in other words, operating rules are usually unknown.

This class (Class B) will contain by far the largest part of the
elevators in almost any city or large town. For this reason the
behavior of the various door-protective devices in Class B buildings
is a matter of vital interest. For this class of service the most
simple and rugged type of mechanical interlock or electromechan-
ical device is desirable. Almost invariably electric door contacts
seem to give trouble, under the combination of heavy duty and
little or no attention.

For elevators in Class C buildings the requirements which are to
be met are not so severe. Any device that will stand up under
occasional use, but with almost entire lack of attention, will
probably give satisfaction. Most mechanical devices give fairly
good service, although in some cases which were noted they have
worn rapidly owing to lack of lubrication. Electromechanical
and contact devices give fair service provided they are used often
enough to prevent the contacts from oxidizing and corroding.
This class is probably smaller than either Classes A or B, and is
confined very generally to smaller cities and towns. Frequently
in Class C installations may be found various types of makeshift
devices, some of which fail to accomplish the purpose for which
they were intended.

6. TABULATION OF RESULTS OF SURVEY

The data regarding interlocks and electric contacts given on the
following pages were obtained by examining substantially all of
the elevators in many of the smaller cities and towns of Penn-
sylvania and New Jersey and all of the elevators in representative
blocks in the larger cities. In uptown New York the blocks were

1 2 Technologic Papers of the Bureau of Standards

between Fifth Avenue and Broadway and Thirty-sixth and Forty-
fifth Streets. In downtown New York both sides of Broadway
were covered for a number of blocks. This was done in an effort
to observe an average condition, and it is believed that the data

given here are typical of the various towns or sections in which
inspections were made.

Summary of Conditions of Interlocking Devices in Pennsylvania (Exclusive of First-

Class Cities)

GENERAL ANALYSIS

Elevators inspected 79

Landings inspected 513

Cars not provided with car-gate contacts (required by Pennsylvania law) ... 20

Per cent not up to requirements of Pennsylvania law 25. 2

Landings provided with interlocks 513

Landings provided with interlocks found to be inoperative 47

Per cent of landings with interlocks inoperative 9. 2

ANALYSIS BY TYPE OF DEVICE

Landings provided with mechanical interlocks 244

Landings with mechanical interlocks inoperative 26

Per cent of landings with mechanical interlocks inoperative 10. 6

Landings provided with electromechanical interlocks 269

Landings provided with electromechanical interlocks found to be inoperative . 2 r

Per cent electromechanical interlocks found to be inoperative 7. 8

ANALYSIS BY CLASS OF BUILDINGS IN WHICH ELEVATORS ARE LOCATED

CLASS A

Landings in this class 149

Landings with interlocks inoperative 10

Per cent of landings with interlocks inoperative 6. 7

CLASS B

Landings in this class 313

Landings with interlocks inoperative 36

Per cent of landings with interlocks inoperative zz. 5

CLASS C

Landings in this class 51

Landings with interlocks inoperative i

Per cent of landings with interlocks inoperative 2. o

Summary of Conditions of Interlocking Devices in New Jersey

GENERAL ANALYSIS

Elevators inspected 189

Landings inspected 1466

Landings with no hoistway-door protection 227

Per cent of landings with no hoistway-door protection 15- 5

Landings not provided with mechanical or electromechanical interlocks (as

required by New Jersey law) 559

Elevator Interlock Report 13

Per cent of landings not provided with mechanical or electromechanical

interlocks (as required by New Jersey law) 44. 8

Landings provided with interlocks or contacts 1239

Landings with interlocks or contacts inoperative 73

Per cent of landings with interlocks or contacts inoperative 5. 2

ANALYSIS BY TYPE OF DEVICE

Landings provided with mechanical interlocks 243

Landings provided with mechanical interlocks found to be inoperative 29

Per cent of mechanical interlocks found to be inoperative 11.9

Landings provided with electric contacts * 329

Landings provided with electric contacts found to be inoperative * 44

Per cent of electric contacts found to be inoperative * 13. 3

Landings provided with electromechanical interlocks 2 667

Landings provided with electromechanical interlocks found to be inopera-
tive 2 o

Per cent of electromechanical interlocks found to be inoperative 2 o

ANALYSIS BY CLASS OF BUILDING IN WHICH ELEVATORS ARE LOCATED

CLASS A

Landings in this class 845

Landings with interlocks or contacts inoperative 19

Per cent of landings with interlocks or contacts inoperative a. 2

CLASS B

Landings in this class 350

Landings with interlocks or contacts inoperative 53

Per cent of landings with interlocks or contacts inoperative 15. i

CLASS c

Landings in this class 44

Landings with interlocks or contacts inoperative i

Per cent of landings with interlocks or contacts inoperative 2. 3

Summary of Conditions of Interlocking Devices in Philadelphia

[NOTE. Municipal regulations require the use of mechanical or undercar contact electromechanical inter-
locks.]

GENERAL ANALYSIS

Elevators inspected 49

Landings inspected 503

Landings provided with interlocks 503

Landings with interlocks inoperative 66

Per cent of landings with interlocks inoperative 13.0

ANALYSIS BY CLASS OF BUILDING IN WHICH ELEVATORS ARE LOCATED

CLASS A

Landings in this class 404

Landings with interlocks inoperative 9

Per cent of landings with interlocks inoperative 2. 2

1 While contact devices without door-interlocking mechanisms are not permitted under the New Jersey
law, a number of such devices were found. Some of these devices were installed prior to the enactment of
the law and will, no doubt, eventually be changed to comply with the legal requirements.

1 Seventy-five per cent of the electromechanical devices were found in one "Class A" group, where the
maintenance service was excellent

14 Technologic Papers of the Bureau of Standards

CLASS B

Landings in this class _ 99

Landings with interlocks inoperative 3 57

Landings with interlocks inoperative (final) 28

Per cent of landings with interlocks inoperative 56. o

Per cent of landings with interlocks inoperative (final) a 8. o

Summary of Conditions of Interlocking Devices in Uptown New York City 4

GENERAL ANALYSIS

Elevators inspected 294

Landings inspected 3, 043

Landings provided with interlocks or contacts 229

Per cent of landings provided with interlocks or contacts 7. 5

Landings with interlocks or contacts inoperative 50

Per cent of landings with interlocks or contacts inoperative ai. 8

ANALYSIS BY TYPE OF DEVICE

Landings provided with electric contacts 190

Landings with inoperative electric contacts 37

Per cent of landings with inoperative electric contacts 19. a

Landings provided with electromechanical interlocks 39

Landings provided with electromechanical interlocks inoperative 13

Per cent of landings with electromechanical interlocks inoperative 33-3

DATA ON CAR-GATE CONTACTS

Cars provided with car-gate contacts aa

Car-gate contacts in operating condition 10

Per cent of car-gate contacts in operating condition 45-5

Car-gate contacts tied up or plugged 7

Per cent of car-gate contacts tied up or plugged 31. 8

Car-gate contacts broken or defective 5

Per cent of car-gate contacts broken or defective 23. 7

Summary of Conditions of Interlocking Devices in Downtown New York City *

GENERAL ANALYSIS

Elevators inspected 241

Landings inspected 5, 304

Landings provided with interlocks or contacts i, 926

Per cent of landings provided with interlocks or contacts 36. 4

Landings with interlocks or contacts inoperative a

Per cent of landings with interlocks or contacts inoperative a 10

ANALYSIS BY TYPE OF DEVICE

Landings provided with mechanical interlocks 893

Landings with mechanical interlocks inoperative i

Per cent of landings with mechanical interlocks inoperative 0.10

Landings provided with electromechanical interlocks i, 014

Landings with electromechanical interlocks inoperative i

* As 29 of the 57 defective landings were in a single group of buildings which had evidently been over-
looked by the inspector, this estate was omitted from the final statistics as not being representative.

4 Only one mechanical interlock was found in the particular uptown section inspected, so that statistics
on this type are not given. Buildings equipped with interlocks or contacts in this tabulation may be r-
garded with very few exceptions as Class B.

6 All of these downtown buildings provided with interlocks or contacts in this tabulation ar CWi A

Elevator Interlock Report 15

Per cent of landings with electromechanical interlocks inoperative o. 10

Landings provided with electric contacts 20

Landings provided with electric contacts inoperative o

Summary of an Inspection to Determine the Effectiveness of Emergency Releases,

Uptown New York City 6

ELECTROMECHANICAL DEVICES

Elevators inspected 43

Landings inspected 504

Landings working satisfactorily 225

Per cent of landings working satisfactorily 44-6

Landings where elevators were running with emergency switch thrown; no

electrical or mechanical trouble 148

Per cent of landings unprotected, due to emergency switch being thrown. . . 29. 4
Landings where elevators were running with emergency switch thrown or

system disconnected, due to electrical or mechanical breakdown 131

Per cent of landings unprotected, due to electrical or mechanical breakdown. 26. o

This survey was made to determine to what extent the emer-
gency release is used as a means of defeating the purpose of door-
protective devices.

The emergency releases were all of the two-pole, push-button
type. Most of them were without a cover glass or even a means
of holding a cover glass. The results of this survey show that an
emergency release of this type will be misused. The only type
which should be permitted is that in which the operator is re-
quired to hold the emergency release in the emergency operating
position.

Practically all of the devices inspected on this survey were
poorly designed and cheaply made, which may in part account
for the large number of defective landings noted.

7. DISCUSSION OF SURVEY

RELATION OF LAW ENFORCEMENT TO ELEVATOR SAFETY.
There is a marked difference between the condition of elevators
in a State or city where the law or code relating to elevators is
strictly enforced and a State or city where the law does not have
the backing of an active and thorough administrative organiza-
tion. In many parts of one State the law calling for interlocks
did not seem to be generally known, and even in the larger cities
no particular efforts had been made to enforce it. In many cases
it has been through the notification given the building owners by
insurance inspectors that the devices have been installed. By
way of contrast, however, in another State there was not a single
elevator examined that was not equipped with the required inter-

6 Nearly all of these are Class B buildings.

1 6 Technologic Papers of the Bureau of Standards

lock, although in a few electric-elevator installations the addi-
tional car-door contact which was required by law was lacking.

Perhaps the most badly needed addition to present State rules
and city ordinances is a set of simple, brief, and concise operating
rules to be posted in every elevator under the jurisdiction of the
particular State or city. Certain cities have already provided for
the licensing of car operators. The passing of an examination is
necessary before the applicant is granted a license. In this way
it is possible to discourage the operation of elevators by the
ignorant or uninstructed. Unfortunately, during the war it was
deemed necessary to waive this ruling in certain cases, and the
strict enforcement of this rule has not yet been insisted upon.

PERFORMANCE OF INTERLOCKS IN VARIOUS CLASSES OF BUILD-
INGS. In regard to the performance of interlocking devices, there
seems to be but little difference between the mechanical and
electromechanical interlocks. Many installations, both mechan-
ical and electromechanical, were met with in Philadelphia that
had been giving satisfactory service for periods of 15 years and
upward, with a cost for repairs and renewals not exceeding $i per
landing for the entire period, while numerous installations met
with in the smaller cities of Pennsylvania were found to be in good
condition after 10 years or more of service.

As might be expected as the result of the combination of hard
service with little or no maintenance, the Class B installations in
every case have made the poorest showing, but even here the
percentage of installations in working order indicates that the
protection afforded by such devices is decidedly worth while.

For Class A installations the average percentage of devices in
working order was 98. When the fact that an interlock may be
called on to function several hundred times a day is taken into
consideration, this percentage must be considered remarkable.

Class C installations were generally in fairly good condition,
due mainly to light service requirements.

INTERLOCK INSTALLATIONS IN LARGE OFFICE BUILDINGS.
The results of the inspection in the down-town section of New
York City brings forth two points of particular interest.

First, the relatively large number of interlock installations.
While interlocks are not required by the city ordinances, over
one- third of the landings inspected had been so safeguarded.

Second, the remarkably low number (two) of defective landings
found despite the severe duty imposed on the elevators in the

Elevator Interlock Report 17

large office buildings down town. Excellent maintenance service
and the carefully designed and well-built interlocks which pre-
dominate in this section are, no doubt, largely responsible for
this fine showing.

SUGGESTIONS FOR IMPROVEMENT IN DESIGN. From a general
survey of results obtained it would seem that there is room for
considerable improvement in the types of interlocking devices.
Of the hundreds of elevators inspected none were equipped with
a mechanical interlock in which the four vital functions of unlock-
ing hoistway door, locking car mechanism, unlocking car mecha-
nism, and locking the door are performed by means of positive
mechanical motion. In other words, at least one, and generally
more, of these functions are accomplished by means of springs
or the force of gravity, or a combination of the two. An inter-
lock in which all four of these functions are performed without
the aid of a spring or the action of gravity should be not par-
ticularly difficult of design. Rules to be drafted should, how-
ever, take cognizance of present well-designed apparatus and
should be so worded as to not hinder improvement in design or
new designs.

Door contacts, while usually of ample current-carrying capac-
ity, are seldom rugged enough to stand up under the impact and
vibration of the hoistway door, where they are actuated by the
impact of the door itself. Another characteristic feature about
them is that in nearly every case the making and breaking of
the current is dependent directly upon and is accomplished at
the same speed as the opening and closing of the door. Many
such devices, if the door fails to latch, are left in but slight con-
tact and may produce an arc which will rapidly destroy the con-
tact surfaces. The use of a sequence coil or a quick make-and-
break switch will do much to eliminate such arcing and pitting.

There are several well-designed devices with switches that are
not subject to door impact and which give long and satisfactory
service when made a part of a substantial interlock mechanism.
Well-designed mechanical locks are also available. A substantial
door-locking mechanism is necessary whether the method of
interlocking the car is electrical or mechanical. The door-
locking function should be so interconnected with the car inter-
lock that the car can not be started until the door is locked in the
closed position.

1 8 Technologic Papers of the Bureau of Standards

There is considerable need for some sound engineering work
in connection with the proper design of interlocks. Many of
the devices on the market were designed without due regard for
the stresses set up by door impact, lack of alignment, and abuse
of equipment at the hands of careless operators. Such devices
are generally sold at a low price, the manufacturer depending
upon this low price to obtain business. In many cases such
devices fail after a short period of service and are, in the end,
more expensive than a well-designed and carefully installed out-
fit, the initial cost of which would have been greater.

III. SUMMARY OF ADVANTAGES AND DISADVANTAGES OF
VARIOUS TYPES OF DEVICES

The following tabular arrangements set forth the advantages
and disadvantages of the various types of elevator door safety
devices and the characteristic methods of failure of the various
types of devices for the various classes of service:

Elevator Interlock Report

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Elevator Interlock Report

Public accidents.

IV. ELEVATOR-ACCIDENT STATISTICS

There are attached a .number of tables of elevator statistics
obtained from various sources. The public accidents have been
separated from the industrial accidents where this was possible,
and the classification has been made to show the number of acci-
dents by causes.

Accidents have been classified as public, semipublic, or indus-
trial, according to the nature of the occupancy of the building, as

follows :

Hotel

Apartment house
Department store (patrons).
Office building

[Hospital

Semipublic accidents {_

IGarage

Industrial accidents. . .

(Mercantile establishment (employees only).

The accidents have been further grouped into shaft-door and
nonshaft-door accidents and the percentages computed on this
basis for each table. For convenience in analysis the statistics
have been divided into groups according to sources, as noted below
and shown in the tables following:

Group I. General: Reports of accidents received through clip-
ping bureaus. These cover the entire United States.

Group II. State industrial reports of State industrial commis-
sions. These are taken from records of industrial accidents and
do not cover accidents to the general public.

Group III. Municipal statistics from records of coroners of
cities or records of elevator inspection departments.

1. GROUP I. GENERAL

TABLE 1. Elevator Accidents Reported Through Clipping Bureaus by the Public
Press of the United States, January, 1913, to July, 1918

tal

Non

fatal

Cause

Public

Semi-
public

Indus-
trial

Not
classi-
fied

Public

Semi-
public

Indus-
trial

Not
classi-
fied.

Fell into shaft from landing
floor or due to motion of the
car

150

198

121

181

Crashed between car and sill
of landing floor or frame of

150

168

107

138

150

330

486

Cause not given

Total

407

528

569

779

Technologic Papers of the Bureau of Standards

TABLE 2. Summary from Table 1 : Entire United States from Newspaper Clippings,
January, 1913, to July, 1918

Classification and cause

Fatal

Nonfatal

Public:

Per cent

Nonshaft-door accidents 26. 2 60

Shaft-door accidents-
Fell into shaft 36.9 21.3

Crushed between car and sill or frame of door 36. 9 18. 7

Total 100 100

Semipublic:

Nonshaft-door accidents 30. 5 44. 5

Shaft -door accidents-
Fell Into shaft 41. 7 37

Crushed between car and sill or frame of door 27. 8 18. 5

Total 100 100

Industrial:

Nonshaft-door accidents 49.6 59

Shaft -doer accidents-
Fell into shaft 37. 4 23. 2

Crushed between car and sill or frame of door 13 17.8

Total. . . 100 100

2. GROUP H. REPORTS FROM STATE INDUSTRIAL COMMISSIONS OR
DEPARTMENTS OF LABOR

TABLE 3. Elevator Compensable Industrial Accidents, New York State, June 1,

1914, to July 1, 1915

[From data submitted by the New York Industrial Commission. N. O. C. Not otherwise classified]
NONFATAL ELEVATOR ACCIDENTS

Cause

Num-
ber

Per

cent

Cause

Num-
her

Per
cent

Caught between floor and car.

Falls into shaft from floor

Caught between shaft and car .

Fall of car

Struck by car (N. O. C.)

Gates (N. O. C.)

Unknown

Objects falling into shaft

Cables breaking

Caught by machinery

Caught by cable

Falls into shaft from car. . .

113
63
26
41
36
39
33
61
32
25
25
13

19.6
10.9
4.5
7.1
6.3
6.7
5.7
10.0
5.6
4.3
4.3
2.3

Caught between car and gate

Struck by counterweight

Objects falling down shaft from car.

Struck by car in pit

Machinery breaking

Load catching between car and

shaft

Cables unwinding

Struck while on top of car

Total.

577

2.3
1.9
2.3
1.5

1.7

1.0
.7
.7

100.0

Elevator Interlock Report

TABLE 3. Elevator Compensable Industrial Accidents, New York State, June 1
1914, to July I, 1915 Continued

FATAL ELEVATOR ACCIDENTS

Cause.

Num-
ber.

Per
cent.

Cause.

Num-
ber.

Per

cent.

Falls into shaft from floor

27.7

Unknown .. .. ....

2 1

Caught between shaft and car. . . .

12.8

Machinery breaking

2 1

Caught between floor and car
Struck by car (N. O. C.)

5
4

10.6
8.6

Load catching between car and
shaft

2.1

Fall of car

6 4

Csble unwinding

2.1

Falls into shaft fronj car

6.4

Struck while on top of car

2 1

Total

100.0

Caught between car and gate

4.2

TABLE 4. Elevator Accidents in Industries and Mercantile Establishments in the
State of Pennsylvania, 1918

[From statistics furnished by the Department of Labor and Industry of Pennsylvania]

Fatal

Nonfatal

Total

Number

Percent

Serious:
Number

Minor:
Number

Total

Number

Percent

Number

Per cent

Cable breaking

4
1
3
17
3
2
1
1
5
7
1
5

8
2
6
34
6
4
2
2
10
14
2
10

27
9
43
134
30
10
10
10
35
34
15
31

29
7
49
171
36
7
17
35
26
27
16
50

56
16
92
305
66
17
27
45
61
61
31
81

6.5
1.7
10.7
35.7
7.8
2.0
3.1
5.3
7.1
7.1
3.6
9.4

60
17
95
322
69
19
28
46
66
68
32
86

6.6
1.9
10.5
35.5
7.6
2.0
3.1
5.1
7.3
7.5
3.5
9.4

Cable unwinding

Cable, caught by

Car, caught by

Car, struck by

Counterweight, struck by
Defective equipment

Entering or leaving car

Fall of car

Fall of person

Falling objects ...

AO others

TotaL

100

388

470

858

100.0

908

100.0

24 Technologic Papers of the Bureau of Standards

TABLE 5. Wisconsin Industrial Accidents on Elevators
[From published reports of the Wisconsin Industrial Commission, 1915-1917]

Cause

Fatal

Nonfatal

Total

Number

Per cent

Number

Per cent

Number

Per cent

Falling from floor down shaft

5
2

35.6
14.3

24
55
14
14
14
16
4
4
10
22
18
6
4

11.7
26.8
6.9
6.9
6.9
7.8
1.9
1.9
4.9
10.7
8.8
2.9
1.9

29
57
14
15
15
17
4
5
10
22
20
7
4

13.2
26.0
6.4
6.9
6.9
7.7
1.8
2.3
4.6
10.1
9.1
3.2
1.8

Platform floor catching person

Caught between cage and side

Struck by objects falling dowri shaft

1
1

7.1
7.1
7.1

Car struck person

Car fall big

Car sudden start or stop

Struck by counterweight

7.1

Hoisting cable striking person

Hoisting machinery catching person

Platform and gate catching person

14.4
7.1

Falls from car

Load or other object catching person

Total

100.0

205

100.0

219

100.0

TABLE 6. Elevator Accidents in Industries in Massachusetts (Freight and
Passenger, Insured, not Insured, and Common Law Rights)

[From published reports of Massachusetts Industrial Accident Board

Total

Cause

July 1,1913, to
June 30, 1914

July 1, 1914, to
June 30, 1915

July 1, 1915, to
June 30, 1916

July 1, 1916, to
June 30, 1917

Fatal

Nonfatal

Fatal

Non-
fatal

Fatal

Non-
fatal

Fatal

Non-
fatal

Fatal

Non-
fatal

Num-
ber

Per
cent

Num-
ber

Per
cent

Caught in ma-

chin err

1.5

179

6.92

Caught be-

tween car

and shaft

186

204

289

38.8

728

28.1

Caught under-

neath or on

top of car. . . .

10.5

3.67

Falling car

4.48

179

6.87

Falling down

shaft (person)

32.9

235

9.08

Struck by fall-

ing object

1.5

161

6.22

Caught by fire

hatch or trap .

.96

Miscellaneous

284

265

213

228

10.5

990

38.2

Total

591

676

597

728

100.0

2,592

100.0

NOTB. The classification used here is not as suitable for grouping the hoistway-door accidents into two
general classes as the other tables presented.

Elevator Interlock Report

TABLE 7. Analysis of State Elevator Statistics

INDUSTRIAL ELEVATOR ACCIDENTS, NEW YORK STATE, JUNE 1, 1914, TO JULY 1, 1915

Cause

Fatal

Nontatal

If onshaft-door accidents

Per cent
51 1

Percent
64 9

Shaft-door accidents:
Fell into shaft

34.1

13 2

Caught between floor and* car or gate and car

14 8

21 9

Total

100

INDUSTRIAL AND MERCANTILE ELEVATOR ACCIDENTS, PENNSYLVANIA, 1918

If onshflft-door accidents

51 9

Shaft-door accidents:
Fell into shaft

7 1

Caught by car and entering or leaving car

Total.

100

INDUSTRIAL ELEVATOR ACCIDENTS, WISCONSIN, 1915-1917

Nonshaft-door accidents

35 7

52 7

Shaft-door accidents:
Fell into shaft

35.6

11 7

Platform floor catching person

platform and gate catching person

28 7

35 6

Total

100

INDUSTRIAL ELEVATOR ACCIDENTS, MASSACHUSETTS, JULY 1, 1913, TO JUNE 30, 1917,

INCLUSIVE

If onshaft-door accidents

28.3

62 82

Shaft -door accidents:
Fell into shaft

32.9

9 Q8

Caught between car and shaft

38 8

28 1

Total

100

3. GROUP m. MUNICIPAL STATISTICS
TABLE 8. Philadelphia Elevator Accidents

iype

Injured

Killed

Injured

Killed

Injured

Killed

Injured

Killed

Injured

'Killed

Passenger :<>
Electric

Hydraulic

Freight:
Electric

Hydraulic

Belt

Hand

Sling

Total

Interlocks required by law on passenger elevators.

Technologic Papers of the Bureau of Standards

TABLE 9. Fatal Accidents on the Elevators of Borough of Manhattan, New York
City, 1907 to 1918, Inclusive

[From coroner's reports]

Cause

Number

Per cent

Fell down shaft 292 40.5

Crushed between moving car and sill or frame of shaft door 335 46. 5

Miscellaneous (broken cables, falling cars, workmen in the shaft struck by moving

car.etc.) ... 94 13

Total 721 100

TABLE 10. Fatal Elevator Accidents, Cook County, HI., 1904 to March, 1916,

Inclusive

[From coroner's reports]
Cause Number Per cent

Fell down elevator shaft 169 42. 2

Crushed between elevator and floor, wall, door, etc 152 37. 9

Killed by falling elevator 24 6.0

Struck by elevator 23 5. 7

Crushed by counterweights 12 3.

Crushed in elevator 8 2.

Struck by falling objects other than elevator 1. 7

Crushed by machinery of elevator 4 1.0

Unknown how accident occurred 2 .5

Total... 401 100.0

TABLE 11. Summary of Elevator Accidents of Two of the Largest American Cities

[Reported from coroner's records]

Fatal

Borough of Manhattan, New York City,
1907 to 1918, inclusive, public and
industrial:

Nonshaft-door accidents

Shaft -door accidents-
Fell down shaft

Crushed between car and sill
or frame of shaft door

Cook County, 111., 1904 to March, 1916,
inclusive:

Per cent
13

40.5
46.5

Nonshaft-door accidents

Shaft -door accidents

Fell down shaft

Crushed between elevator and
floor, wall, door, etc

Total..

100

Total..

Per cent
19.9

42.2

37.9
100

An analysis of these statistics shows that the weighted average
percentage of accidents presented in the preceding tables, due to
causes originating from the lack of an interlocking device with
which is combined a substantial lock, is as follows :

Elevator Interlock Report 27

Fatal accidents to public, per cent of total accidents given in preceding tables. 73. 8

Fatal accidents to industrial employees, per cent of total 54

Nonfatal accidents to public, per cent of total 40

Nonfatal accidents to industrial employees, per cent of total 53. 2

The statistics show that the largest number of accidents is
caused by falling down the shaft, the weighted average percentage
of the total fatalities to the public from this cause being 36.9,
and to industrial employees being 36. In the case of nonfatalities
these percentages are, public 21.3, industrial employees 14.7. It
should be noted that the percentage of all fatalities from falls
is about the same for both classifications, public and industrial.
This is a strong indictment of the ordinary door latch, and the
results of the survey bear out the conclusion reached by a study
of accident statistics. A substantial lock should, therefore, be
made a part of every interlock and the ordinary door latch dis-
carded. A somewhat minor point which should not be neglected
in the design of interlocks, since it bears directly on the hazard
of falling down the shaft, is the possibility of opening the door
from the landing side when the car is passing a landing. Devices
which permit this should not be installed.

The next most prolific cause of accidents is the crushing hazard ;
that is, the possibility of being crushed between car and sill of
landing floor or frame of door. The average percentage of the
total fatalities to the public from this cause is 36.9 and to indus-
trial employees 18. In the case of nonfatalities the percentages
are, public 18.7, industrial employees 38.5.

These values, on comparison with those for causes originating
within the shaft, show the necessity of interlocking the movement
of the car with the opening and locking of the door. Not only
should the interlocking function be associated with the closing
of the door but also the locking of the door, inasmuch as the
unlocked door exposes the user to the hazard of falling into the
shaft.

Another cause of accident resulting from lack of interlock
devices is stepping into the shaft under the mistaken idea that
the car is at the landing. A study of 978 elevator fatalities
showed that i .3 per cent of the accidents were due to this cause,
and of 1386 nonfatalities the percentage was 0.9. This is a real
hazard and is comparable with many of the accident percentages
due to causes originating within the shaft. It is recommended
that provision be made against it.

28 Technologic Papers of the Bureau of Standards

Perhaps the most striking figures are those of the city of Phila-
delphia, which show the remarkable results obtained by the
compulsory use of interlocks in a large city. Of the four people
killed on passenger elevators in 1918 only one was a passenger,
the other three being elevator operators or mechanics. The fact
that there was not a passenger nor an operator killed in an electric
elevator during the entire year of 1918 is a remarkable tribute to
the effectiveness of the interlocks required by the Philadelphia
law and to the administration of the code in force in that city.
The contrast in the experience with freight elevators, for which
interlocks are not required, is very marked.

The following requirements cover, in general, the desirable
interlock features to be incorporated into an elevator code. It
is urgently recommended, however, that the latest issue of the
A. S. M. E. Elevator Code be consulted as to the exact wording;
so that greater uniformity may be secured and that advantage
may be taken of criticisms of earlier drafts of that code.

V. SUGGESTED REQUIREMENTS TO BE INCLUDED IN AN

ELEVATOR CODE

The following definitions and specifications are submitted as
tentative suggestions suitable for inclusion in an elevator code
and are intended to give adequate protection and to mitigate the
hazards previously set forth. From the evidence thus far accumu-
lated the use of a hoistway-door interlock seems advisable, and
this protection should be required on passenger elevators at least.

The material presented in this report was gathered for use in
formulating an elevator safety code and was placed at the dis-
posal of the joint committee which was formulating a national
code for the American Society of Mechanical Engineers and with
which the Bureau of Standards has been cooperating. The
definitions and specifications which follow and those tentatively
adopted by the committee agree in all essentials. Any evidence
tending to support or modify these conclusions will be gladly
received by the Bureau of Standards.

1. DEFINITIONS

HOISTWAY-DOOR INTERLOCK. A hoistway-door interlock is a
device the purpose of which is

i. To prevent the normal operation of the car, except by the
use of a leveling device, unless (a) (door unit system) the hoist-

Elevator Interlock Report 29

way door opposite which the car is standing is locked in the
closed position; or (6) (hoistway unit system) every hoistway
door is locked in the closed position.

A hoistway door or gate shall be considered locked in the closed position when
within 4 inches of the full closure. If in this position, and any other up to full closure,
the door or gate can not be opened from the landing side more than 4 inches.

Interlocks which permit the starting of the car before the door is fully closed shall
be so equipped that except when the door is locked in the position of full closure
the door or gate can be opened from the landing side to the position approximately
4 inches from full closure.

2. To prevent the opening of a hoistway door (except by use
of a key) from the landing side when the car is passing a landing;
except when the car-control mechanism is in the "stop" position.

HOISTWAY-DOOR ELECTRIC CONTACT. A hoistway-door electric
contact is an electrical device the purpose of which is to prevent
the normal operation of the car except by the use of a leveling
device unless (a) (door unit system) the hoistway door opposite
which the car is standing is in the closed position, or (6) (hoistway
unit system) every hoistway door is in the closed position.

EMERGENCY RELEASE. An emergency release is a device the
purpose of which is to make hoistway-door electric contacts or
hoistway-door interlocks inoperative.

2. SPECIFICATIONS

HOISTWAY-DOOR INTERLOCK SPECIFICATIONS. (a) The pre-
vention of the operation of the car by a hoistway-door interlock
shall not be dependent on the action of springs in tension nor
solely upon the completion or maintenance of one electrical
circuit.

(6) The agency used to perform any interlocking function shall
be such that even without lubrication of the mechanism the
intended functioning of the device will be completely performed.

(c) The locking of the hoistway door and the interlocking of
the car control shall be accomplished by an interconnection
between the parts of the device. This interconnection may be
mechanical, electrical, hydraulic, or pneumatic.

(d) It shall be necessary to accomplish the locking of the hoist-
way door opposite which the car is standing before the car can be
moved by normal operation.

This paragraph applies to both the door unit and the hoistway
unit system.

(e) If without damage to, removal of, or interference with any
part of the elevator or hoistway equipment the door opposite

30 Technologic Papers of the Bureau of Standards

which the car is standing becomes unlocked, it shall be impossible
to start the car by normal operation.

HoisTWAY-DooR ELECTRIC CONTACT SPECIFICATIONS. (a) The
prevention of the operation of the car by an electric contact shall
not be dependent on the action of springs in tension nor solely
upon the completion or maintenance of one electric circuit. The
failure of the device shall manifest itself by preventing the starting
of the elevator from the landing.

(6) The device shall be such that without lubrication of the
mechanism the intended functioning will be completely performed.

EMERGENCY RELEASE. (a) The emergency release shall be in
the elevator car, plainly visible to the occupants and reasonably,
but not easily, accessible to the operator.

(6) To operate under emergency conditions, it shall be necessary
for the operator to hold the emergency release in the emergency
position. The emergency release shall be so constructed and
installed that it can not be readily tampered with or "plugged"
in the emergency position.

(c) Rods, connections, and wiring used in the operation of the
emergency release that are accessible from the car shall be inclosed
to prevent their being tampered with readily.

WASHINGTON, May 14, 1921.

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