1、Lessons Learned Entry: 1221Lesson Info:a71 Lesson Number: 1221a71 Lesson Date: 1981-01-05a71 Submitting Organization: LARCa71 Submitted by: James R. RookerSubject: Mobile A-Frames Description of Driving Event: A 5-ton mobile A-Frame was being used to lift a 8450 No. piece of research hardware from a
2、 lower floor level to the wind tunnel floor through a slot in the wind tunnel floor. Due to the constrained operational space and complex geometry of the hardware, the lift was not through the C.G. of the hardware. During the lift operation, the C.G. rapidly shifted causing the lift line to fall out
3、side of the A-frame base dimension. This caused the A-frame to rapidly topple over and inflict fatal injuries to a bystander. This same lift had been successfully completed on a previous occasion using lateral movement restraints, but there appeared to be no loading on these restraints; therefore, t
4、hey were not used for this lift. During the mishap investigation, an observation was made that the wheels were only rated for 3000 No. each which implies that all four wheels must be equally loaded to safely support the 10000 No. rated load. If the lift line moved from a vertical position (e.g. load
5、 swinging during transit) the wheels would be unequally loaded and the load could exceed the wheel rated loading.Lesson(s) Learned: A-frames can rapidly become dangerously unstable with lateral movements of the load. Portable A-frame wheels could be sized to carry only one fourth of the rated load.R
6、ecommendation(s): A-frames should be constrained to a 2.5 to 1 height-to-base ratio which will allow the lifting line to be approximately 11 degrees from vertical before an unsafe condition could occur. A-frame base support devices should be provided for A-frames with wheels to preclude overturn due
7、 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-to the loss of a wheel when lifting its rated load. A-frames should be positioned directly over the object to be lifted with the lifting line vertical, the hoist-to-object attachment vertical, or the s
8、ling vertical. Lifts should be performed through the center of gravity of the object to be lifted or lateral movement restraints should be imposed to maintain the lifting line vertical. If the lifted object is to be transported by the A-frame, the center of gravity of the object should be as low as
9、practical and lateral restraints imposed to maintain the lifting line vertical during transport. At no time during the use of A-frames should the lifting line be allowed to get outside of the A-frame base dimensions. A-frames should be marked with their load capacity rating. Evidence of Recurrence C
10、ontrol Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Ground Equipmenta71 Ground Operationsa71 Hardwarea71 Lifting DevicesAdditional Info: Provided by IHSNot for Res
11、aleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2002-06-27a71 Approval Name: Leslie J. Johnsona71 Approval Organization: LARCa71 Approval Phone Number: 757-864-9409Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
