U.S. Department of Labor
Occupational Safety and Health Administration
Directorate of Construction
Reported Prepared by
Mohammad Ayud, PE
Dinesh Shah, PE
The Directorate of Construction, OSHA National Office, was requested to provide assistance in the investigation and causal determination of the July 23, 2003 fatal collapse of a scaffold at the construction site of the Hathaway Bridge in Panama City, FL. The scaffold was located on the westbound bridge under construction. A structural engineer from the Office of Engineering, Directorate of Construction, OSHA National office visited the incident site on August 26, 2003 and on subsequent dates. Each time, he was accompanied by the Compliance Officer from the Jacksonville OSHA Area Office.
The incident occurred in the morning hours of July 23, 2003 as a work crew of four employees was placing grout bags and other materials on the cantilever section of the scaffold. The scaffold was custom-designed for the project by United Form Services, Inc., of Neodesha, KS and was known as "Custom Cantilever Style Finishing Work Platform." As the grout bags were placed on the cantilever section of the scaffold, the scaffold suddenly failed, causing the four employees to slip and fall into the water. One employee was killed but the other three survived with varying degrees of injuries. Figures 4, 5 and 6 show a similar scaffold not involved in the incident.
Granite Construction Company, the general contractor of the bridge under construction, contracted with United Forms Services (UFS) to design, fabricate, deliver and erect a custom-designed finishing platform for the bridge. UFS designed the scaffold which was later fabricated by Young's Welding of Chanute, KS. Two such platforms were delivered, assembled and erected at the site under direct supervision of UFS. UFS designed the scaffold for a rated load of 2,000 pounds, including the weight of workers, equipment, etc.
UFS drawings El thru E6 of November, 2002 bearing the signature of a professional engineer provided the details of structural steel framing of the scaffold. The framing consisted of a 44' long cantilever platform, 6' wide. The cantilever platform was supported by a 36' high vertical truss, also 6' wide. The truss at the top was supported by two outrigger beams spaced at 6' on centers, and supported by two wheel struts spaced at 12' on center on top of the bridge, see Figure 1. To counteract the effects of the cantilever, counterweights were placed on outrigger beams above the bridge floor. 1 3/4" diameter steel braces were provided to transfer the loads at each corner, see Figure 1 and 2. The braces at each end were connected by ratchet shoes, see Figure 4, and 5. The upper ratchet shoe was connected to a 6 x 3/8 x 1'-3" steel plate, see Figure 6. The steel plate was connected to the bottom flange of the outrigger beams using A325 bolts. As discussed earlier, the cantilever platform was designed for a total live load of 2,000 pounds uniformly distributed over the cantilever span, including the weights of all employees and all other miscellaneous weights (Figure 2, 3 and 7).
Field observation of the collapsed scaffold indicated that the critical failure occurred at the 3/8" connection plate of the ratchets to the bottom flange of the outrigger beams.
We conducted independent structural analyses to determine the causal factors that could have contributed to the collapse of the scaffold under the loads placed on it immediately before the incident. The following loads were considered in the analysis:
UFS rated the platform for a maximum load of 2,000 pounds. This was specifically included in the general notes of their contract drawings (Figure 3) that "Design load on this work platform is 8 men anywhere on the platform or 2,000 pounds distributed at 50 pounds per square foot." UFS also stated elsewhere on the drawing that "2000 pound total live load on the buggy includes the load on the work platform, access platform and ladders (impact is not included)." The magnitude of the load placed on the scaffold on the day of the incident was clearly far greater than the rated capacity of the scaffold. A load of approximately 6,000 pounds was placed on the scaffold that had a rated capacity of only 2,000 pounds. In fact at the time of the incident, workers were continuing to place additional loads on the scaffold until it collapsed.
OSHA requires that all scaffolds and components be designed for their dead loads and for four times the intended load without failure. UFS's drawings stated that the design for the scaffold met OSHA requirements. Our structural analysis, however, indicated that the scaffold did not meet the requirements of the OSHA standard. The 3/8" ratchet connecting plate was overstressed over 200% under four times the intended load. The scaffold could not support its dead load and four times the rated load, (i.e., 4 x 2,000 pounds = 8,000 pounds) without failure. If the scaffold was properly designed and fabricated to meet the OSHA standard, the placement of 6,000 pounds on the scaffold would not have caused the scaffold to collapse. The collapse should not have occurred until the load reached 8,000 pounds.
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