Elevator Maintenance and Inspection: Recommendations, Regulations and Codes: 1880-1940

The beginning of an investigation exploring a global history of elevator (and escalator and moving walk) codes and standards.

This article was first presented at the 2019 International Elevator & Escalator Symposium in Las Vegas. For more information on December 6-7, 2021’s event in Amsterdam and to participate, visit International Elevator & Escalator Symposium

The 60-year period from 1880 to 1940 witnessed the slow but steady appearance of recommendations, regulations and codes that addressed elevator maintenance and inspection. The history of these activities has traditionally focused on the development of the ASME A17.1 code. While the importance and influence of this code was significant, the U.S. was not alone in its pursuit of rules designed to govern elevator safety, maintenance and inspection. During the period under investigation, other countries pursued similar goals and developed a series of regulatory documents that reflected both an awareness of American efforts, as well as parallel efforts throughout Europe. This article will trace the history of these codes and focus on the related topics of maintenance and inspection. This investigation will address which — according to the various codes, components or systems — required inspection, the nature of the inspections of new systems (prior to use), the proposed frequency of inspections and maintenance, how inspections were to be conducted and who was responsible for conducting inspections.

1880-1900

In November 1878, a draft of a new ordinance was presented to the Chicago City Council. The ordinance, a proposed revision to the city’s existing building regulations, concerned the creation of the Office of Inspector of Elevators. The ordinance was approved at the council’s January 1879 meeting and required that inspections occur at least once every six months to ensure all “elevator shafts and doors are in a perfectly safe condition and in accordance with the provisions of this ordinance.”[1] While the initial ordinance did not include any selection criteria for hiring an inspector, this omission was corrected in the 1881 Municipal Code of the City of Chicago, which stated the “inspector of elevators shall be an experienced architect, builder or mechanic competent to perform the duties of the office to which he is appointed.”[2] The inspector’s duties were defined as follows:

“He shall, as often as once in six months, carefully examine and inspect all hoistways in which an elevator shall be used or operated, and the doors and shafts in connection therewith; and also examine and inspect all passenger and freight elevators, cars or platforms used and operated in any building in the city of Chicago, other than a private dwelling house, and report to the commissioner the condition of each hoistway and elevator.”[2]

If the inspector found that an elevator was unsafe, he could require it be taken out of service until repairs were made. It is important to note the focus of the inspection — and the ordinance — was shaft doors (or trap doors over jack holes in industrial settings) and shaft construction. The primary concerns were preventing people from falling down shafts and fire safety (ensuring shafts were built of brick or other fire-resistant materials). The ordinance did not require the examination of elevator machines, ropes or safeties.

In 1887, new city building laws were amended to suggest an expansion of the areas of concern with regard to inspection: “The superintendent of buildings. . . shall make regulations for the inspection of passenger elevators with a view to the safety of passengers. . . . The regulations so made shall require any repairs found necessary upon inspection to be made without delay.”[3] The actual ordinance, however, remained focused on shaft construction and doors, thus offering no guidance on what else would, or could, be inspected to ensure “passenger safety.”

Until the mid-1890s, Chicago remained unique in having a dedicated elevator inspector. This changed in 1894 when the city of Philadelphia approved an ordinance establishing designated elevator inspectors:

“The director of the Department of Public Safety, with the approval of the mayor, shall appoint two additional inspectors in the Bureau of Boiler Inspection, who shall be competent mechanical engineers, whose duty it shall be to inspect at least once in every three months all elevators used for the purpose of carrying either passengers or freight, or passengers and freight, to see that the same are in perfect working order, and that all the parts are in good condition and repair.”[4]

The ordinance also empowered inspectors to shut down an elevator “if any defects be found to exist in any part or parts of any passenger or freight, or passenger and freight elevator which would tend to impair the safety or endanger life.”[4] However, once again, the text of the ordinance focused primarily on elevator doors and shafts and provided no guidance regarding the inspection of other “parts” of an elevator system.

The content of contemporary elevator regulations in Europe paralleled those found in the United States. Their primary focus was doors and shafts, with the emphasis on elevators used in industrial settings. A fundamental shift occurred in 1893 with the publication of Ordinance on Elevator Construction and Operation in Berlin in Germany.[5] While, like its American counterparts, the ordinance applied to a single metropolitan area, it differed significantly in its scope. In addition to addressing shaft construction and door safety, the ordinance included sections on indicators, controls, stop limits, counterweights, factors of safety for hoisting ropes, safe operating speeds and inspections. All new elevators were to be inspected “before being put into service. . . to determine whether” they complied with the ordinance’s provisions.[5] Following an inspection, a report was issued that included a written description, drawings and a copy of the calculations used to determine the elevator’s load-bearing capacity (presumably these materials would have been supplied by the manufacturer). While the ordinance clearly stated that all inspections were to be carried out by “experts,” it did not identify their qualifications. It was simply noted that a list of approved experts could be found at Berlin police stations and that “the selection of the expert. . . [was] left to the owner of the elevator.”[5] All freight elevators were to be inspected every two years, while passenger elevators required annual inspections. Because the purpose of an inspection was to determine if an elevator remained in compliance with the ordinance, it may be reasonable to assume this prompted the development of appropriate maintenance programs.

Six years after the publication of this ordinance, one of the first national elevator codes appeared in what was, perhaps, an unlikely location. In 1899, Denmark approved an Executive Order that addressed the construction and operation of “mechanically operated elevators and hoists.”[6] While these regulations followed the general outline of the earlier German example, they lacked a similar level of detail. Although the Danish regulations addressed both freight and passenger systems, their primary focus was on freight elevators. Prior to an elevator being placed into service, an inspection was to be conducted by the manufacturer and the Danish Factory Inspectorate to ensure compliance. The order also stated “it goes without saying that, in addition to the regulations contained in this executive order, elevators must further satisfy the demands made by local building authorities in their layout.”[6] This statement was one of the first to acknowledge the challenge presented by requiring that building owners respond to regulations developed at both national and local levels.

The 19th century closed with the publication of the most comprehensive set of regulations to date and, once again, the country of origin was Germany. In September 1899, the State of Prussia approved a General Order Concerning Elevator Installation and Operation.[7] The content of the order was organized into five primary sections: general provisions, passenger elevators, freight elevators, elevator operation and acceptance and inspection. Each section contained a higher level of detail than previous efforts, a fact reflected in the final section, which included detailed specifications for testing brakes and safeties. All safety devices were to be tested individually, with the car carrying the maximum rated load and operating at its maximum permitted downward speed. Additionally, safety grips were expected to be fully activated before the car fell 0.25 m. The inspection period was also lengthened, with all elevators (passenger and freight) subject to inspection every two years. And, as was the case with the earlier regulations, the qualifying attributes of the “experts” who conducted inspections remained a mystery, with the order simply noting, “Experts within the meaning of this ordinance shall be those persons designated as such by the local police authority.”[7]

1901-1920

The first two decades of the 20th century witnessed the continued development of elevator codes and regulations in the United States, across Europe and across the globe. The refinement of German elevator regulations continued throughout this period, while other countries began initial forays into this arena. In 1903, Charles M. Walckenaer published the first critical assessment of French elevator systems, which included (as an appendix) a draft of proposed elevator regulations.[8] The regulations were limited in scope and focused primarily on passenger elevators. They did, however, include a brief reference to maintenance and inspection. Walckenaer proposed, “All parts of the system must be maintained in good condition. In particular, the cables must be replaced in good time, and the operating devices and interlocks must be kept in good working order.”[8] He also proposed that all elevators “must be examined and checked at sufficiently frequent intervals by competent and attentive visitors.” His use of the word “visitors,” rather than “inspectors,” reflects Walckenaer’s recognition that the implementation of his proposed regulations, as well as who would assume responsibility for enforcement, was very much an open question at this time.

In 1906, a set of regulations that emphatically answered the question of who was responsible for elevator inspection and what was required of elevator owners appeared. The regulation’s country of origin serves as a reminder of the global use of vertical-transportation technology in the early 20th century. In December 1906, the Parliament of the State of Victoria in Australia approved An Act to Regulate the Use of Passenger and Other Lifts.[9] The act assigned the responsibility for elevator inspection to the chief inspector of factories, work-rooms and shops, and any inspector employed by his office. While this specificity was matched by the requirement that all elevators in the State of Victoria were required to undergo inspection within 60 days of the new law going into effect, after that point, its implementation was less clear:

“An inspector shall, from time to time, inspect all lifts constructed or used or in course of construction and for that purpose, may, during working hours, enter any building or premises and shall, if required by the owner lessee or occupier, sign and deliver to him a certificate certifying the result of such inspection.”[9]

The purpose of the inspection was to ensure that an elevator was not “dangerous to human life or limb,” and that its design and operation complied with “the regulations under this act.”[9] In fact, the act did not include specific regulations. It did, however, grant Parliament the ability to “make regulations as to the construction inspection and working of lifts.”[9] The official Regulations Under the Lifts Regulation Act of 1906 was approved in April 1907 and included 58 rules — 28 of which referenced the authority of the inspector in determining compliance.[10] The regulations were divided into several sections: “Hydraulic Lifts,” “Belt-Driven, or Other Power Lifts,” “Electric Lifts,” “Fees” and “General.” The technical specificity of these regulations may be illustrated by two rules associated with electric elevators:

“An automatic stop which will instantly break the circuit should the overrun of the car exceed 6 in. shall be fitted to every goods or passenger lift where the inspector so directs. This stop must be made to actuate from the car.

“The electrical controlling gear must be to the approval of the inspector and must be of an efficient type and shall automatically slow down and cut off at either limit of travel. It must operate in a satisfactory manner without causing excessive strain in any part of the apparatus. The electric controls must so operate as to obviate any excessive and deleterious sparking.”[10]

The regulations also provided guidance on the frequency of inspections, suggesting all elevators (freight and passenger) should be inspected every 12 months. In 1908, the State of South Australia approved a similar act and corresponding set of regulations, and, during the following decades, Australian legislators continued the steady expansion and improvement of these codes.

The interest in regulating elevators, particularly with regard to safety, was a critical focus of an investigation undertaken by Italian engineer Luigi Pontiggia in 1910. His work, originally published in L’industria Rivista Tecnica ed Economica Illustrata as a 24-part series of illustrated articles, was published in book form in 1911 as Industrial Elevators: Safety and Use.[11] This work included the first multinational survey and overview of European elevator regulations.[12 & 13] Although Pontiggia included, in an appendix, suggested guidelines for elevator use, he did not endorse the need for the development, at least in Italy, of official “burdensome and prohibitive” regulations.[11] This antiregulatory view was shared by other countries. Interestingly, England had a similar attitude during this period that stood in stark contrast to its Australian compatriots. Other countries, of course, followed a different path. In 1908, Denmark approved a revised version of its 1899 code.[14] The new code included a broader explanation of the inspector’s duties. All elevators were to be inspected every year, and the inspector was to confirm that, in the case of a suspended system, the ropes and safeties met the regulation’s standards. The required rope strength was twice the weight of the car with its maximum capacity load, and the safeties were required to operate within a range of 0.33 m.

The culminating event of the opening decades of the century was the publication of the first American national code, which was the immediate precursor to the A17.1 code (which appeared in 1921). On October 12, 1917, the Elevator Manufacturers Association of the United States formally adopted a code titled Uniform Regulations for the Construction and Installation of Passenger and Freight Elevators.[15 & 16] The code, published later that same year, was 47 pages long and addressed 63 regulatory topics, which were divided into three sections: definitions, new elevator installations and shafts. The rules addressed a wide range of topics, including locking devices on landing doors, car enclosures, shipper ropes, guide rails, signals and shaft construction. The topic of inspection was addressed in terms of the system’s overall design and construction. The goal was to ensure critical components could be easily examined when needed. This ease of access was also directly linked to the need for regular maintenance — although the actual term “maintenance” did not appear in the code:

“Partitions, guards and head room around elevator machines shall be so located as to make all parts of the machines properly accessible for inspection and care.

“Counterweight enclosures shall be provided with removable sections, not less than 2 ft high and the full width of the enclosure, located near the top, for the inspection of counterweights and cables.”

The code did not propose suggested inspection intervals or identify qualifications of inspectors; the authors may have assumed inspection protocols would be determined and defined by local codes.

1921-1940

The first edition of the American A17.1 code appeared in 1921.[17] This event also marked the beginning of an intensive period of investigation that produced four editions of the A17.1 code, published in 1921, 1925, 1931 and 1937, and which produced the first inspector’s manual. The 1921 code included references to inspection that resembled those found in earlier works. However, it departed from these precedents in offering readers the first rule that addressed maintenance. These related topics were addressed in a section titled “Rules for Inspection and Maintenance,” which included four rules: “Responsibility, Inspection, Maintenance, and Care of Installation.” The first rule identified the persons responsible for inspections:

“It shall be the duty of the owner of the property upon which an elevator is or may be installed to specify in any lease which he may execute, the party responsible for the care and maintenance of the elevator. It shall then become the duty of the designated party to make periodic inspections and maintain in proper working order all parts of the elevator installations.”[17]

The general tone and somewhat vague character of this rule was revised in the code’s 1925 edition (this rule remained unchanged in the 1931 and 1937 editions):

“Responsibility for the care, operation, and maintenance should be definitely fixed by statute or ordinance. Where not so fixed, it is recommended leases for buildings specify such responsibility as between owner and lessee. The person responsible for the installation or his agent shall make periodic inspections and maintain in proper working order all parts of the elevator installation.”[18-20]

The revised language thus recognized the existence of local codes and their utility in helping define these critical activities. The 1925 code also defined the roles and responsibilities of elevator manufacturers and owners (language retained in the 1931 and 1937 editions):

“The responsibility of the elevator manufacturer for failure of the elevator or of any part thereof ceases when the elevator has been put in service and has been approved by the municipal, state or other body having legal jurisdiction. The owner or his duly appointed agents should be responsible for the safe operation and proper maintenance of the elevator after it has been put in service and has been approved by the municipal, state or other body having legal jurisdiction.”[18-20]

These statements reiterated the importance of existing regulations outside the A17.1 code that governed elevator design and installation.

The 1921 rule on inspection recommended what should be inspected and when inspections should occur:

“Hoistway door and car gate interlocks, contacts, control apparatus, controller, automatic stop, limit stops, car and counterweight cables, ‘safeties,’ guide rails and elevator machines shall, in passenger elevator installations, be inspected quarterly and, in freight elevator installations, shall be inspected semiannually. Plunger shoes, bypasses and piston rods of hydraulic elevators shall be inspected at least once in three years. Inspection shall be made by a competent person. A certificate of inspection shall be posted in the car, stating the name of the inspector and the date of inspection.”[17]

The proposed inspection timeline, every three months for passenger elevators and every six months for freight elevators, was clearly an aggressive safety schedule. An unknown fact is how this schedule related to or supported existing maintenance contracts between manufacturers and building owners. Changes in the second edition (also found in the third and fourth editions) included the addition of “buffers” and “the lighting of the car and of the machine room” to the list of items needing inspection.[18-20] The revised rule also suggested that passenger elevators and freight elevators be inspected quarterly.

The rule concerning maintenance was essentially the same in all of the first four A17.1 editions:

“Cables, guides and all parts of machinery shall be kept well lubricated. The oil in bearings and gear casings shall be renewed every six months. Pressure tanks of hydraulic elevators shall be tested at least once every three years with hydrostatic pressure fifty (50) per cent in excess of the maximum working pressure.”[17-20]

The only difference was the inclusion in the 1921 code of a statement noting that “the use of a lubricant containing graphite or other opaque substance shall not be permitted on elevator cables.”[17] This statement was omitted from later editions.

Accompanying the 1937 code was a new resource designed to support the implementation of the A17.1 code: The American Recommended Practice for the Inspection of Elevators: Inspectors’ Manual.[21 & 22] The new manual was intended:

“ . . .to serve as a guide for the general use of elevator inspectors. It is based on the requirements of the American Standard Safety Code for Elevators, Dumbwaiters, and Escalators, and reference to the rules of that code is frequently made in the text, but it must be clearly understood that, while representing good practice, both the manual and the code have no legal force. While many legal codes are based upon the American Standard Code, inspectors should be guided by whatever elevator code is legally in force, and the recommendations made herein applied only so far as they harmonize with legal requirements.”[21]

The desire to model “good practice” (what today would be  called “best practice”) to be followed when inspecting elevators prompted the manual’s authors to include a high level of specificity in their recommendations. The manual was divided into two primary parts: “Part I Routine Inspection” (covering existing installations) and “Part II Initial or Data Inspection” (covering new installations). The work associated with existing installations included requiring inspections made from inside the car, from the top of car and overhead, from outside the hoistway, machine inspection, slack-cable inspection and pit inspection. Each inspection type was explained in detail, a fact illustrated by the requirements associated with an inspection made from the top of the car. This included the examination of the counterweight fastening and counterweight buffer, ropes, rope fastenings, rope tension, rope lubrication, slowdown and stop switches, upper limit switch, car clearance, rail surfaces, rail joints and fastenings, rail alignment, and door operators. The examination of new installations addressed 32 items, which included inspections and equipment tests that addressed subjects such as limit-switch and oil-buffer tests, car and counterweight safety tests, and the examination of hoistway dimensions and clearances, pit clearances, car and counterweight clearances, and interlocks.

The appearance of the 1921 A17.1 code, the rapidity with which the next three editions were produced, and the publication of the Inspector’s Manual in 1937 contributed to its popularity and its use as a model for European codes. However, not all new national codes followed this path in their development. The first Italian national code, Regulations for the Installation and Operation of Passenger and Freight Elevators, was approved in 1926.[23] While the code was one of the least proscriptive in Europe (consisting of only 21 rules), seven of the rules concerned inspection and maintenance. All elevators were to “be inspected once a year,” and the inspections were to “be performed by technicians with a civil or industrial engineer diploma.”[23] Maintenance was to be performed by “a competent person or company,” and the designated tasks included “periodic lubrication,” repairs (as needed), semiannual examinations of the hoisting ropes and safety tests.”[23]

In 1933, the Dutch Ministry of Labour, Trade, and Industry published Guidelines for Elevator Safety, which followed the organizational structure of contemporary codes.[24] It included chapters on general provisions, installations, electric passenger and freight elevators, hand-powered freight elevators, paternosters and general operating instructions, as well as a final section titled “Explanatory Statements” that provided guidance on the code’s implementation. Article 169 addressed inspection and maintenance: “A lift must be maintained by a professional at regular intervals; due to the nature of the business, maintenance work must take place after longer or shorter periods of time.”[24] The implementation of Article 169 was predicated on one key factor — the number of times per day the lift was in use:

“a. for lifts with very heavy duty, e.g., with 100 or more startups per hour at certain times of the day, weekly maintenance

b. for lifts with heavy duty, e.g., with 40-100 startups per hour at certain times of the day, a 14-day maintenance schedule

c.for medium-sized lifts, e.g., with 10-40 starts per hour at certain times of the day, monthly maintenance

d. for lifts with light operation, e.g., with a maximum of 10 startups per hour at certain times of the day, bimonthly maintenance”[24]

The origins of this maintenance standard are unclear; however, it may have derived from concerns about the impact of high use on electric motors.

In 1934, the Finnish Ministry of Trade and Industry published Regulations for Elevator Construction, Installation, Use, Maintenance and Inspection, which focused almost exclusively on electric elevators. (There are only three references to hydraulic systems.)[25] The code devoted an entire chapter to the topic of inspection, which addressed the inspection of new and existing elevators. New machines were to be examined by a “competent lift inspector” who was asked to determine if the elevator complied “with the regulations in force and any other conditions that must be regarded as necessary with a view to preventing the danger of accident or fire.”[25] This required testing all of the “safety devices mentioned in the regulations, such as limit switches, speed governors, slack-cable switches, door contacts, alarms and brakes.”[25] The safety gear was to be tested with the car “fully loaded.” Elevators equipped with gripping safety gears were required to undergo drop tests from rest, with the safety operating before the car fell more than 25 cm. Inspections were to occur for passenger and paternoster elevators every two years and for freight elevators every four years.

The first British national regulations, the Code of Practice for the Installation of Lifts and Escalators, was published by the British Building Industries National Council in 1935. An analysis of the code has revealed that its primary source was the contemporary A17.1 code: 22 of the 24 elevator regulations had direct counterparts in the American code.[26 & 27] However, the regulation concerning inspections and maintenance was more British than American:

“A contract of maintenance should be arranged in respect of every lift, preferably with the makers of the lift concerned, with a view to ensuring regular and adequate cleaning, oiling and adjustment service at such intervals as the type of equipment and nature of the service demands. Every power-driven lift, before being put into service, should be covered by insurance, such insurance [coverage] to include for and incorporate regular inspections at least three times per annum by a representative of the insurance office. At least once in every three years, the safety gear and governor switch, if fitted, should be subjected to a running test under maximum load and speed conditions, and a certificate issued on the result of each test. Such certificate, in its most effective form, should be signed by the insurance engineer supervising the test.”[27]

Assuming that elevator manufacturers were best suited to provide regular maintenance followed American industry practices. However, the reliance on “insurance engineers” for inspections aligned with British business standards.

The 1935 edition of the German national code, Ordinance on Elevator Construction and Operation, contained a slight expansion of the inspection regulations found in earlier codes.[28] The initial inspection was to include tests of “all the prescribed safety devices. . . by means of trial runs in each direction with the greatest permissible load. . . [and], in the case of traction-sheave elevators, it shall be ascertained by a trial descent with double load whether the friction between rope and sheave is sufficient.”[28] Passenger elevators were to be inspected every two years, while freight elevators were only subject to inspection every four years. Each inspection was to test and examine the same components covered by the initial inspection. The revised code also added a new requirement. During the period between scheduled inspections, all elevators were subject to one unannounced inspection, which focused on “the general condition of the installation and, in particular, on the condition of the suspensions and the door and control safety devices.”[28]

The 60-year period examined in this article closed with the publication of the first attempt at defining an international set of elevator standards and regulations. In 1939, the International Labour Office published Safety in the Construction and Use of Lifts, a work that was the result of an almost 10-year initiative begun by Italian engineer Francesco Massarelli in 1930.[29 & 30] The project examined materials gathered from Australia, Belgium, Finland, France, Germany, Great Britain, Italy, the Netherlands, Sweden, the Union of South Africa and the United States. While this important work, with its detailed text, extensive bibliography and 98 illustrations, provides unique insights into early elevator codes and regulations, it failed to achieve the goal of defining a set of international rules. The book’s editorial strategy consisted of presenting topics in an essentially neutral manner, often simply noting that different countries occasionally applied different standards. Thus, material on inspection and maintenance found in this work simply echoed that found in earlier codes and offered no new insights.

Conclusion

This article represents one aspect of an investigation exploring a global history of elevator (and escalator and moving walk) codes and standards. While a significant body of material has been collected thus far (as indicated by this article’s existence), more work remains. Numerous countries (and continents) are not represented, and many early codes have not been found or examined. Your author would welcome assistance in the collection of this, often elusive, material so that this important international investigation may continue, and this rich history may be finally (and fully) explored.

References

[1] Proceedings of the City Council of the City of Chicago for Municipal Year 1878-1879. Chicago: Dunn & Heggie (1880)
[2] Municipal Code of the City of Chicago, Chicago: Beach, Barnard & Co. (1881).
[3] Laws Relating to Buildings in the City of New York. New York: Record & Guide (1887).
[4] Ordinances of the City of Philadelphia, from January 1 to December 31, 1894. Philadelphia: Dunlap Printing Company (1895)
[5] “Polizei-Verordnung über die Einrichtung und den Betrieb von Aufzügen (Fahrstühlen) in Berlin.” Deutsche Bauzeitung, Vol. 27, pp. 258-260 (May 1893).
[6] “Bekendtgørelse angaaende Indretningenog Brugen af mekanisk drevne Elevatorer og Hejseværker,” Samling af Love og Anordninger m.v. 1897-1899. Copenhagen: by J.H. Schultz (1900).
[7] “Allgemeine Verfügung vom 4. September 1899, betr. die Einrichtung und den Betrieb von Aufzügen (Fahrstühlen),” Ministerial-Blatt für die gesamte innere Verwaltung in den Königlich Preußischen Staaten, Berlin: J.F. Starde (1899).
[8] Walckenaer, Charles M. “Sécurité des ascenseurs,” Comptes rendus des séances du Conseil d’hygiène (24 July 1903).
[9] The Acts of Parliament Passed in the Sixth Year of the Reign of His Majesty King Edward the Seventh, Being the Third Session of the Twentieth Parliament of the State of Victoria. Melbourne: J. Kemp (1907).
[10] “Regulations Under the Lifts Regulation Act 1906,” The Public Statutes of Victoria. Volume 3: 1906 and 1907. Melbourne: Charles F. Maxwell (1908).
[11] Pontiggia, Luigi. Gli Elevatori Industriali Considerati nei Riguardi della Sicurezza del Loro Esercizio. Milan: Associazione degli Industriali d’Italia (1911).
[12] Gray, Lee. “Early 20th Century European Elevator Regulations (Part One).” ELEVATOR WORLD, January 2018.
[13] Gray, Lee. “Early 20th Century European Elevator Regulations (Conclusion).” ELEVATOR WORLD, February 2018.
[14] “Bekendtgørelse om Indretningen og Brugen af mekanisk drevne Elevatorer og Hejseværker,” Samling af Love, Anordninger, offentlige Kundgørelser, ministerielle Cirkulærer og Skrivelser m.m. for Aaret 1908.
[15] Uniform Regulations for the Construction and Installation of Passenger and Freight Elevators. Elevator Manufacturers Association of the United States (October 1917).
[16] Gray, Lee. “The First Elevator Safety Code: A Mystery,” ELEVATOR WORLD, November 2006.
[17] American Society of Mechanical Engineers. A Code of Safety Standards for the Construction, Operation, and Maintenance of Elevators, Dumbwaiters, and Escalators (1921).
[18] American Engineering Standards Committee. Safety Code for Elevators, Dumbwaiters, and Escalators (1925).
[19] American Standards Association. American Standard Safety Code for Elevators, Dumbwaiters, and Escalators (1931).
[20] American Standards Association. American Standard Safety Code for Elevators, Dumbwaiters, and Escalators (1937).
[21] American Standards Association. American Recommended Practice for the Inspection of Elevators: Inspectors’ Manual (1937).
[22] Gray, Lee. “The First Elevator Inspectors’ Manual,” ELEVATOR WORLD, February 2014.
[23] “Approvazione del regolamento per l’impianto e l’esercizio degli ascensori per trasporto in servizio privato di persone e di merci accompagnate da persone,” Gazzetta Ufficiale Del Regno D’Italia (9 September 1927).
[24] Leidraad voor Veiligheidsmaatregelen voor Liften, The Hague: Algemeene Landsdrukkerij (1933).
[25] Märäykset Hissien Raakentaamista, Asentamista, Käyttöä, Hoiltoa ja Tarkastusta Varten. Helsinki: Suomalaisen Kirjallisuuden Seuren Kirjapainon Osakeyhtiö (1933).
[26] Gray, Lee. “The 1935 Code of Practice for the Installation of Lifts and Escalators” Proceedings of the 6th Symposium on Lift & Escalator Technologies (2016).
[27] Building Industries National Council. Code of Practice for the Installation of Lifts and Escalators, London (1935).
[28] Carl Heymanns Verlag. Ausführungsanweisung. Polizeiverordnung über die Einrichtung und den Betrieb von Aufzügen. Mit Ausführungsanweisung und den technischen Grundsätzen des deutschen Aufzugsausschusses für den Bau von Aufzügen auf Grund des § 4. Berlin (1935).
[29] Gray, Lee. “The First International Elevator Safety Standards,” Elevator Technology 22. International Association of Elevator Engineers (2018).
[30] International Labour Office. Safety in the Construction and Use of Lifts. Geneva: P.S. King & Son, Ltd. (1939).