Scissor Lift Accident Analysis
 |
| Bob Harrell |
J. Robert "Bob" Harrell is president of Safety Management Services, San Diego,
April 20, 2005 -- In 2003, more than 1,100 construction workers died from accidents on the job, the highest number of fatal accidents the U.S. Department of Labor recorded that year. Often times, an accident can be prevented if an employer properly trains its operators on the potential hazards in the work environment and provides an appropriate action plan if an accident does occur. When an employer fails to provide proper training to its employees, the risk of an accident and injury to the operator and other workers on the jobsite are increased. In the following accident, anything that can go wrong does. Find out how the accident could have been prevented and what steps the operator and employers should have taken.
The accident
The foreman for a roof structure company was driving a scissor lift with the platform elevated in order to install joist hangers on wooden nailers that were secured to the tops of steel joists. Inside the building was a large concrete shear wall with a 2-foot-deep footing around it, which had not been filled with concrete, and the joist hangers were going to be installed above the footing.
As the worker drove forward, the front tires went into the footing, causing the scissor lift to tip over. The operator grabbed the bottom chord of the steel joist, so he wouldn't go down with the machine. As he hung onto the bottom chord of the steel joist, the operator attempted to swing hand-over-hand to a section of the roof where his co-workers could pull him up. As he was attempting to move towards the roof deck, he lost his grip and fell 28 feet onto the frame of the fallen scissor lift. His injuries were so severe that he is no longer able to work in the construction industry.
Preventing the accident
First, the individual should have received qualified training on how to operate the scissor lift. If he had received qualified training, he would have known to inspect the work site for potential hazards before using the scissor lift.
When selecting a trainer, make certain that the individual knows how to operate the equipment, knows the manufacturer's safety requirements, the ANSI A92.6 criteria, and the OSHA regulations. Training should include both classroom and hands-on instructions, and the amount of time spent training should be long enough for a worker to understand and demonstrate that he/she can operate the equipment safely.
With regard to this accident, inspecting the workplace is covered in ANSI A92.6, Section 7. This section states that before the aerial platform is used and during use, the user shall check the area in which the aerial platform is to be used for possible hazards, such as, but not limited to:
- Drop-offs or holes,
- Bumps and floor obstructions,
- Debris,
- Overhead obstructions and high voltage conductors,
- Hazardous locations,
- Inadequate surface and support to withstand all load forces imposed by the aerial platform in all operation configurations,
- Wind and weather conditions,
- Presence of unauthorized persons, and
- Other possible unsafe conditions.
Avoiding the hazard
Since the hazard could not be readily eliminated, one way the employer could have avoided the hazard is by asking the general contractor to pour the footing for the shear wall. This would have provided a safe surface for the scissor lift to drive on. If the footing could not be poured prior to the installation of the roof structure, effective wheel stops or barricades could have been placed around the footing.
Placing a wheel stop near the footing would have given the operator an advanced warning of the hazard. Wheel stops should be large enough to prohibit the scissor lift from driving over them. Plywood, lumber, or pallets of material can serve as a wheel stop or warning barricade. However, a guardrail around the footing would not be an effective wheel stop. A guardrail system is required to be capable of withstanding a 200-pound force, and a scissor lift driving into a guardrail system would break the guardrail with very little effort.
What about fall protection equipment?
Upon evaluation of fall protection equipment used with a scissor lift, we know that the anchorage point for a fall arrest system has to be able to support 5,000 pounds without failure if the anchorage is not engineered, or 3,600 pounds if a registered professional engineer evaluates the anchorage and determines that it is strong enough (it has a 2:1 safety factor), based on a qualified person's evaluation and determinations.
For illustration purposes, let's assume that the maximum arresting force on a worker's body is 900 pounds, based on the type of full body harness and energy absorbing lanyard being used. Using the 2:1 safety factor, the anchorage for fall arrest would have to be capable of supporting 1,800 pounds without failure. Will an anchorage point inside the scissor lift platform support 1,800 pounds of force?
If the worker is using a fall arrest system, which allows a maximum 6-foot freefall before the energy absorber starts to deploy, it is possible that a deck ring installed by the scissor lift manufacturer can support 1,800 pounds of force. However, the scissor lift manufacturer allows a maximum side force on the platform of 50 to 100 pounds. Therefore, a worker falling out of the scissor lift platform will violate the side force safety criteria, and the worker will be tethered to the falling scissor lift. He may even end up under the scissor lift, which would result in the scissor lift falling on him and crushing him.
Can fall restraint be used?
With fall restraint, a worker is attached to an anchorage that will not allow him to free fall below the level where he is standing. This allows one to walk up to an unprotected deck or platform edge but not fall over. The anchorage strength for fall restraint is four times the maximum force that can be applied to the anchorage. If a worker was tethered to a fall restraint anchorage when a scissor lift tips over, the worker would fall because he's still attached to the scissor lift and be injured.
Before requiring a worker to attach to the scissor lift with any type of fall protection equipment, know the scissor lift manufacturer's requirements, including side-loading limitations, and ensure that the worker is capable of identifying hazards and potential hazards in the work environment.
When an employer fails to provide proper training to its employees, the risk of an accident and injury to the operator and other workers on the jobsite are increased. But with proper training and an action plan, most hazards on the job can be eliminated.
