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Mobile Cranes

by Pat Stark, CHST, USF Safety FL-OSHA Consultation

Around the nation in the last year there have been several well-reported crane collapses or crane upsets that have occurred—some resulting in the deaths of workers and bystanders. On July 18 2008 a huge mobile crane collapsed at a Houston, TX oil refinery, killing four workers and injuring seven others. In New York City, two crane incidents in 2008 killed nine persons. In 2008 in Miami, a 7-ton section of a crane dropped 30-stories, killing two workers and injuring at least five others. In Dallas there were at least two crane incidents—one of them involved the snapping of the wire rope which caused the hook assembly to fall and crush a worker. In the Orlando area in July 2008 there was a crane upset during a tree-removal service operation. In this instance no one was apparently hurt, although a home was damaged, and the crane operator apparently ran for the hills and couldn’t be immediately found.

By asking a few questions of the crane operator and conducting an assessment of the crane and the rigging during the jobsite survey or inspection, certain positive or negative aspects can be revealed. We don’t have to have the knowledge of a qualified crane operator to gain an insight on the safe operation of the crane.

One place to start can be the general contractor or the builder, if either is available. Have they checked to see if the particular crane(s) on their project have had their periodic (at least annual) inspection, as per OSHA standards (CFR 29 1926.550(a)(6). Does the crane company or the crane operator have this certificate? What about daily inspections (usually performed by the crane operator)? Are these in writing and are they available for review? OSHA construction standards requires these crane inspections as stated: “The employer shall designate a competent person who shall inspect all machinery and equipment prior to each use, and during use, to make sure it is in safe operating condition.” If deficiencies or defective parts are found during these daily inspections they’re supposed to be repaired or replaced before the crane is operated—as per CFR 29 1926.550(a)(5). Sometimes enquiring about these inspections can reveal information about the particular crane, the crane company and/or the operator. And, if the general contractor, or whomever is leasing or renting the crane isn’t asking these types of questions, why not? They can save themselves quite a bit of heartache if they were to begin to ask for some of this inspection material prior to the crane mobilizing on site. If the crane is to be on site for a period of time arrangements can be made by the company leasing or renting the crane to follow-up on the operator’s daily inspection routine to hold the operator accountable for this important aspect of safe crane operation.

On a recent commercial construction project there were two mobile hydraulic cranes on the site, both rented by different contractors, although both cranes from the same crane company. This was new construction, basically sandy soil and it was wet from a recent rain storm. Neither crane was using blocks or cribbing under their float pads. Only one of these cranes had the blocks available on the bed of the crane, but the operator chose not to use them, stating the ground was compacted. This same crane had a large crack in one of the outrigger float pads and when this was pointed out to the operator he stated something to the affect of: “Yeah, I’m aware of this. I’ve made a note of it in my previous inspections.” The other hydraulic mobile crane’s outrigger pads were basically sunk into the soft, wet, sandy soil; there was no blocking or cribbing available. The synthetic slings used by one of these cranes had numerous tears in the sling and one sling was missing the required capacity tag. Both of these conditions did not meet minimum OSHA rigging standards, CFR 29 1926.251(e). The general contractor stated they had checked on the annual inspection criteria for these cranes, but did not realize they should follow-up on the crane’s daily inspection criteria.

David V. MacCollum states in his book “Crane Hazards and Their Prevention,” that he projects that a crane upset occurs about every 10,000 hours of crane use. He states that “nearly 75% of these upsets were the result of error-provocative circumstances that caused the operator to inadvertently exceed the crane’s lifting capacity. He breaks down these upsets by various causes, the majority (39%) being caused by the crane “making a swing with outriggers retracted”.

OSHA’s “Mobile Crane Inspection Guidelines for OSHA Compliance Officers” (available on the OSHA website www.osha.gov and once there, use their search for Cranes and hoisting equipment to find this document) has considerable information on safe crane operations and inspections. In this piece, OSHA states: “A crane's load rating is generally developed for operations under ideal conditions, i.e., a level firm surface. Unlevel surfaces or soft ground therefore must be avoided. In areas where soft ground poses a support problem for stability, mats and or blocking should be used to distribute a crane's load and maintain a level stable condition.” And, in Bob’s Rigging and Crane Handbook, author Bob DeBenedictis states that “much of the weight of the crane and load can be transmitted to only one outrigger. Since the area of the outrigger float is relatively small it generates high pressure.” He then uses an example of a 150 ton truck crane at maximum load can put a maximum load of 250,000 lbs on one outrigger. He uses a note from the Manitowoc Company that states that the ground pressure on a 3 ft. x 3 ft. outrigger float pad alone would be 193 psi. This psi would change dramatically to 59 psi if a 5 ft. x 5 ft. mat was used under this lone outrigger float pad. This is quite a difference in weight displacement, and can possibly be the difference in a crane upset.

Ronald M. Ward, once an active member of Central Florida ASSE, who was a crane inspector, trainer and was involved in many crane accident investigations, developed a diagram of a crane that pointed out five points of safety on mobile cranes. They were:

  1. Hoist line centered over the center of gravity of the load
  2. Know the weight of the load
  3. Know the radius
  4. Firm support
  5. Crane level

These points and the inspection requirements of these cranes can be useful tools where cranes are in use.