Standard Interpretations - (Archived) Table of Contents|
September 9, 1993
MEMORANDUM FOR: John B. Miles Jr., Regional Administrator Region I FROM: Charles Culver, Director Office of Construction and Engineering SUBJECT: Christmas TreeingThis is in response to your memoranda of July 21 and August 12, 1993 to this office regarding the issue of "Christmas Treeing." Attached to your memorandum of July 21, 1993 was a diagram of a method of attaching tandem loads, which your office has agreed to as an acceptable method in Region I.
We are providing the following discussion for your consideration. The Directorate of Safety Standards Programs and the Directorate of Compliance Programs reviewed and provided comments on this material. The discussion addresses technical considerations associated with christmas treeing. We understand that the Directorate of Compliance Programs is preparing a policy memo addressing this issue.
We talked to several members of the Steel Erectors Association of America and the National Erectors Association. Most all the non- union steel erectors and a majority of the union steel erectors favor christmas treeing as they believe it to be efficient and productive. In fact, they stated that on many of their jobs they had successfully employed christmas treeing during the past several years and continue to do so. When asked about the danger of exposing the connectors to the overhead loads, there was a unanimous reply that when properly rigged, the risk is non- existent. It was also asserted by way of justification that even in the case of hoisting of one beam, the connectors were always at risk at one point or another of being under the load immediately before connecting the beam or when the beam was being hoisted and swung at the construction site. They also said that to their knowledge a very few accidents have taken place involving christmas treeing.
The International Association of Bridge, Structural and Ornamental Iron Workers, on the other hand, opposes christmas treeing on the basis of the risk of ironworkers being struck or crushed by the load above.
Christmas treeing has been a controversial subject since its inception some 20 years ago. Considerable thought has been given in the past by the OSHA, erection contractors (union and non-union), crane manufacturers, the union mentioned above, and others. All recognize the hazards which the practice produces and there appears to be a consensus among those concerned that while the practice should not be totally prohibited, adequate precautions must be taken in a planned manner to ensure the safety of workers during christmas treeing. The concerns related to the method of lifting two or more loads at a time are two fold. The first pertains to the engineering issues, i.e. the magnitude of the loads lifted, their stability under lifting conditions, factor of safety, capacity of the crane and the rigging etc. The second relates to the personnel safety issue, i.e. the potential hazards the practice creates of working under the load. The engineering concerns of christmas treeing e.g., crane capacity, the balance of loads during lifting and the method of rigging can be satisfactorily resolved. For individual projects, before christmas treeing is undertaken, the weights and the centers of gravity of the beams could be calculated, and the rigging system with independent lines could be engineered with a factor of safety of five or more and the beams could be spaced eight or nine feet apart. A number of configurations could be designed which would give an adequate factor of safety.
Christmas treeing could indeed be productive and efficient on projects when erecting floor or roof filler beams, all of the same length and weight with similar details at each end of the beams. In large industrial projects where the location of the crane is much farther away from the bay under erection, christmas treeing could also prove to be efficient. Further, the practice reduces the total number of swings the crane makes in each project, thus reducing the risk of exposing the workers located in the vicinity of the crane or in the path of travel of the load. However, the real issue lies in the hazard of exposing the connector to the loads above him as the load may either strike the connector or drop on him due to the failure of rigging or malfunctioning of the crane. In all the different configurations we studied, the risk is always present to a varying degree including the diagram you attached in your memo of July 21, 1993. When the method of christmas treeing is employed to transport steel members from one storage area to another, the hazards are generally minimal as the task does not involve carrying the loads over people and can be safely undertaken with due precaution.
When two or more steel members are lifted during steel erection, the connectors while connecting the lower beam are exposed to working under the higher beam/beams. The intent of OSHA's standards has always been to protect such employees from this potential hazard. A recent OSHA promulgation removes any confusion which may have existed in the past by reiterating that employees will not be exposed to loads over them. On June 30, 1993, OSHA published in the Federal Register 29 CFR Parts 1910 and 1926 "Incorporation of General Industry Safety and Health Standards Applicable to Construction Work and Technical Amendments; Final Rules." This includes the following regulation: 1926.550(a)(19) which states "All employees shall be kept clear of loads about to be lifted and of suspended loads." It is our interpretation that this applies to all modes of construction including christmas treeing, if the employees are so exposed.
In the past, OSHA Standard 1926.550(b)(2) referred to ANSI Standard B30.5 - 1968 entitled "Safety Code for Crawler, Locomotive, and Truck Cranes" Section 5.3.3.f under "Moving Load" which stated that "the operation should avoid carrying loads over people."
In 1926.701(e) in dealing with the hazards of lifting and lowering concrete buckets in concrete and masonry construction, the OSHA standard categorically prohibits any employee working under such loads. However, in recognition that it is sometimes necessary for elevated buckets to be routed over the heads of workers, OSHA requires "to the extent practical" buckets be routed so that no employee or the fewest number of workers are exposed to the hazard of the falling bucket. In regard to precast concrete, OSHA requires in 1926.704(e) that: "No employee shall be permitted under precast concrete members being lifted or tilted into position except those employees required for the erection of those members".
Further, the practice is discouraged in the field by safety associations and some crane manufacturers. For example FMC Operating Safety Manual states:
1. "Don't lift more than one separately rigged load at a time, even if both loads combined don't exceed the crane's capacity. Your full attention cannot be given to both loads, creating a dangerous situation."
Crane User's Safety Manual - Construction Industry Manufacturers Association states:
1. "Be sure everyone is in the clear before swinging or moving in any direction. Never swing or position hook or load over ground crew or truck cab.
2. Never hoist two or more separately rigged loads in one lift, even though the combined load is within the rated capacity.
Crane Handbook - Construction Safety Association of Ontario states:
1. "Do not hoist two or more separately rigged loads in one lift, even though the combined load is within the crane's rated capacity."
There is also some agreement in the crane industry that the practice of tandem lifting should be discouraged. A number of crane manufacturers furnish the Construction Industry Manufacturers Association Manual, "Safety Manual for Users, Operators and Maintenance Personnel" to crane users and owners, and their policy is to prohibit hoisting two or more separately rigged loads (christmas treeing) in one lift. Some of the manufacturers prohibiting such practices are:
Avis Industrial Corporation/Badger Construction Equipment Company Grove Worldwide Koehring Co./Koehring Cranes and Excavators (Brand Name: Koehring, Loreing, Northwest and Bantam. Note Bantam no longer manufactured) Komatsu Dresser Company (Brand Name: Galion) Link Belt Construction Equipment Company Terex Corporation/North West Engineering The American Crane Corporation JLG Industries
The following companies, however, do not prohibit tandem lifting:
Air Technical Industries Broderson Manufacturing Corporation Little Giant Crane and Shove Inc. Manitowoc Company Inc./ Manitowoc Engineering Co. Mannesmann DeMag Corporation Pettibone Corporation PPM Corporation
The Structural Ironworkers Manual V - Volume 1 prepared by the International Association of Bridge, Structural and Ornamental Iron Workers also addresses the issue of christmas treeing and states that the practice of lifting tandem loads is acceptable as long as "adequate safety precautions" are taken to protect employees. It recommended that the "Tandem loads should be handled in the following manner: (1) tandem loads of structural steel shall be permitted for the purposes of moving steel from storage point to storage point when adequate safety precautions are taken to insure that no employee is in a hazardous position; (2) Tandem loads of structural steel for the purpose of erecting steel shall only be permitted in extremely unusual and absolutely necessary situations concerning which prior agreement must be reached with the qualified safety representative of the employees, to insure that no employees will be placed in a hazardous position by utilization of this method." The above Manual recognizes the hazards, but does not completely prohibit the practice. It permits christmas treeing in "unusual and absolute necessary conditions" with "adequate safety precautions."
Of interest also are the number of reported injuries and fatalities due to this practice as reported to OSHA. During the search of the accidents involving christmas treeing, only three were discovered for the period 1984 - 1993. They are:
(a) On 3/11/92, in Raleigh, NC a rigger was hooking up steel beams onto a "christmas tree lift with bullchokers;" where the crane hook was hooked to one main (longer) load line with several cable slings attached at intervals below the crane hook. The "bullchoker" attachments to the main line were covered by a metal reinforcing "bull-ring." The rigger had hooked up the first two beams of the christmas tree lift and went to hook up a third one while the first two were being raised by the crane. The second beam got caught on the "bull-ring" of the lower attachment on the main cable causing the beam to slip off and fall across the rigger's legs;
(b) On 7/20/90, in Austin, TX a connector was crushed between the first beam and the beam above him as he was bent over to disconnect the first choker from the bottom beam on the "christmas tree lift on bullchokers". The crane operator "had taken his eyes off of the connector for a few seconds, felt the load shift and quickly hit the brake after the load had dropped 7 to 8 feet crushing the connector; and
(c) On 4/23/86, in St. Louis, MO, after connecting a series of beams of a christmas tree lift, an employee fell 54 feet when he attempted to disengage a lower empty hook that got caught on the lower flange of the beam in which the connector was located. The beam rolled as the hook became disengaged causing the employee to lose his balance and fall.
As is evident from above, OSHA, union steel erectors, non-union steel erectors, the International Association of Bridge, Structural and Ornamental Iron Workers and some crane manufacturers have differing views on the subject of christmas treeing. With the recent publication in the Federal Register of a Notice to form a Negotiated Rulemaking Committee to revise the steel erection standard-Subpart R, we believe that the christmas treeing issue should be considered in the negotiations by the committee, if and when the committee is approved by the Secretary of Labor.
CLEARLY, THE CONNECTOR IN STEEL AND PRE-CAST CONCRETE ERECTION IS EXPOSED TO OVERHEAD LOAD AT ONE TIME OR ANOTHER, EVEN IF ONLY ONE LOAD IS LIFTED. THE FUNDAMENTAL QUESTION, THEREFORE, IS SHOULD THE CONNECTOR BE EXPOSED TO MULTIPLE LOADS, THUS INCREASING HIS EXPOSURE AND RISK, TO MEET THE ECONOMIC DEMANDS OF THE TRADE. IT APPEARS THAT THERE IS AN ELEMENT OF TRADE OFF BETWEEN RISKS INVOLVED AND EFFICIENCY AND PRODUCTIVITY OF THE TRADE. THIS TRADE OFF IS A POLICY ISSUE FOR THE ASSISTANT SECRETARY.
Until such time that this policy issue is resolved and the Directorate of Compliance Programs formulates a policy addressing this issue, we believe that a decision whether to permit christmas treeing, or disallow it, should be made on a case by case basis by the Region, considering the factors discussed above. In case a decision is made by the Region to allow christmas treeing, we recommend that the steel erector be required to meet the following conditions:
o He must obtain permission from the manufacturer of the crane being used if that manufacturer prohibits christmas treeing.
o He must perform calculations indicating that there is an adequate factor of safety for all the rigging components.
If your office has questions or needs any clarifications, please do not hesitate to call us at 202-219-8644.
CC: Patricia Clark Roger Clark
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