Construction work is hazardous and can lead to occupational injury and disease (Burkhart and others 1993). The U.S. construction industry has had the highest rate of injury of any major industry group in the Bureau of Labor Statistics annual survey (Bureau of Labor Statistics 1997). Mobile cranes are the backbone of the U.S. construction industry. MacCollum, a recognized authority on crane hazards, has estimated that cranes are involved in 25 to 33% of fatal injuries in construction and maintenance (MacCollum 1993).
The type and number of injuries related to cranes are difficult to quantify, because reported statistics on work-related injuries usually group cranes in larger categories such as “industrial vehicles and equipment” or “equipment and machinery.” According to the Bureau of Labor Statistics (BLS), the category “industrial vehicles and equipment” accounts for 17% of fatal injuries in U.S. construction (Bureau of Labor Statistics 1993). But the proportion of injuries actually involving construction vehicles and equipment is probably greater.
A study of OSHA reports by Hinze and Bren (1996) found that cranes were reported to be involved in 108 (38%) of 284 fatal electrical injuries in the construction industry that involved heavy equipment. (OSHA is the U.S. Occupational Safety and Health Administration.)
The proportion of accidents involving cranes that result in a death or serious injury is unknown. A study in Finland showed that about 12% of accidents involving cranes result in death or permanent disability (Hakkinen 1978).
MacCollum (1980) lists 13 common failure modes of cranes:
1. Overloading
2. Side pull
3. Outrigger failure
4. Hoist limitations
5. Two-blocking
6. Killer hooks [without a throat latch]
7. Boom buckling
8. Upset/Overturn
9. Unintentional turntable turning
10. Oversteer/crabbing
11. Control confusion
12. Access/egress
13. Power-line contact
In addition, serious injuries involving cranes can occur as a result of:
14. Improper assembly or dismantling
15. Rigging failure and fall of load or lifting tackle
16. Being struck by a moving load
17. Accidents related to manlifts
18. Working or standing within the swing radius of a cab or counterweight.
Note: “Two-blocking” occurs when the traveling block suspended by the crane cables is pulled up into the stationary block at the tip of the crane, causing the cable to separate and dropping the traveling block and the load. “Killer hooks” are crane hooks that lack a mechanism for keeping the load sling in the hook, if the load should bounce or the sling move.
There are engineering controls for prevention of crane accidents. Anti two-blocking devices, outrigger extension sensing systems, overload sensors, and limit switches can eliminate or reduce certain failure modes (Jarasunas 1987). Warning devices and limit switches increase safety by providing more information to the operator and reducing the need for guesswork. However, it is unlikely that engineering controls will make crane operation a simple matter.
