Topic: Safety during rescue chain use
Objective: Explain significant safety considerations for rescue chain users
Task: The rescue team shall understand the safety aspects of grades of rescue chain, working load limits, hooks‚ fly-off‚ direction and the importance of conducting visual inspections of rescue chain
Not all chain is created equal and, yes, a chain is only as strong as its weakest link. For rescuer safety, it’s important that the various grades of chain are understood, so chain can be used most effectively.
Chain grades indicate the load rating of the chain and hook. The higher a chain’s grade number, the more load the chain will support safely.
Common grades for chain that’s typically used by rescue personnel include Grade 70, 80 and 100 and appropriately rated hooks. Most safety and health authorities, such as state or federal Occupational Safety and Health Administration (OSHA) agencies, require Grade 80 chain or stronger to be used any time there’s what they consider to be an overhead lifting situation. You should familiarize yourself with regulations that apply to your jurisdiction regarding chain grades and the definition of overhead lifting.
Working load limits
For chain with 3/8-inch-diameter links—which is probably the most common size of rescue chain that’s used in the United States—the chain manufacturer first determines the breaking strength, or maximum load, that the chain can sustain up to its point of failure.
The manufacturer then establishes a safe working load limit (WLL), which always will be a lower number. For chain, many manufacturers typically use a 4:1 safety ratio of failure load vs. WLL. Rescue responders should have their chain WLL memorized. Across the chain industry, 3/8-inch-diameter G7 rescue chain, also known as Grade 70 chain, has a safe WLL of 6,600 lbs. G8, or Grade 80, 3/8-inch-diameter chain has a WLL of 7,100 lbs., which reflects an approximate 7 percent strength increase over Grade 70 chain. The WLL of G10, or Grade 100, 3/8-inch-diameter chain is 8,800 lbs.
Not exceeding the WLL means intentionally preserving an adequate safety factor for personnel.
However, responders must realize that the rated WLL of new chain is measured in what is called a vertical arrangement: Manufacturers pull a straight length of chain until it breaks. Real-world rescue applications, with bends, curves or twists in the chain, can result in unexpected chain or hook failure. The 4:1 safety factor also can diminish if a chain shows signs of abuse, is shock loaded or has other types of physical damage.
So, again, staying at or below the WLL minimizes the risk of chain failure while under load.
A manufacturer can offer so-called tagged chain at an added cost. For a length of chain to be tagged, it’s pulled in a laboratory test machine to a load that’s equal to twice the calculated WLL of the chain. If it passes inspection without damage or failure, a stamped tag is applied to the chain.
If a rescue agency operates with tagged rescue chain, the tag should remain attached throughout the lifespan of the chain. If a tag is lost or damaged, the chain supplier should be contacted for instructions on either retesting and retagging the original chain or replacing it with new equipment.
Hook failure direction
In every attempt to validate hook failure “fly off” direction (completed at B/A Products)—whether grab hook, J-hook or twin hooks of a ratchet strap—when tested to failure, the hook always flew off in the direction of the back, or smooth, side of the hook. Some hooks that flew downward did so at such a violent rate that they took a chunk out of the concrete floor.
Responders must ensure that hooks are placed properly to minimize fly-off under load at an incident scene.
Weld-side vs. nonweld-side
Technical rescue personnel are instructed to place a grab hook on the smooth, or nonweld, side of the chain link when connecting chain at an incident scene. The explanation: This avoids putting pressure or stress on the weld itself. Destructive testing that was conducted by this author showed that, although it’s nice to do this hook arrangement, it isn’t a must-do requirement.
Multiple destructive chain and grab hook tests that were carried out revealed that, although placing the hook on the smooth side of the link might be a good idea, it made no significant difference in the load that the chain and hook could support.
Under controlled test conditions, when pulled to failure at more than five times the safe WLL, placing the grab hook on the weld or nonweld side of the chain link resulted in no significant difference. With Grade 70 chain and grab hooks that have a WLL of 6,600 lbs., for example, failure occurred typically between 33,000–36,000 lbs. of load regardless of grab hook direction across the link of chain. The testing did conclusively prove that, when the load that’s applied to the chain and grab hook remained at or below the safe 6,600-lb. WLL of the chain, weld-side or nonweld-side grab hook placement made no difference. Intentionally overloading to two times the WLL did result in nicks and slight damage to both the grab hook and several links of chain.
Visual chain inspection
Regular visual and physical inspections of rescue chain pre- and post-use might be on a daily, weekly or monthly basis. They should be consistent, comply with the manufacturer’s procedures and be documented.
During the visual inspection process, when one or more links of rescue chain shows evidence of stretching, bending, thinning or any deformity, the chain should be removed from service and disposed of according to department protocols.
Excessive wear of a link in a chain, a worn hook, nicks or gouges also are indicators for removal. Chain or hook storage in a moist, nonwatertight compartment or inside a metal chain container could result in excessive pitting, corrosion or rusting of the metal.
The bottom line for rescuer safety: If any condition is observed during the department’s established visual inspection process that causes doubt within the mind of the examiner as to whether the chain or hook should remain in service, take it out of service, dispose of it and replace it with new equipment in the rescue inventory.