Document EJa6Y66o8qp5GRLy34wZYk2N

strength or elasticity of materials, and de terioration of materials due to wear or othei causes The primary caution legardmg the use of safety belts, as with other personal protective equipment, is to see that they are worn and used correctly A safety belt is worthless unless it is being worn at the time that a fall is possible It should also be securely buckled and worn tight enough to prevent any possibility of the man's slipping out of it Lifelines Lifelines should be seemed above the point of operation to an anchorage or structural member capable of supporting a minimum dead weight of 5400 pounds For most lifelines, mamla rope of X-in diameter or nylon rope of Ji-in diameter is recommended Nylon is more resistant to wear or abrasion than is mamla and is also more resistant to some chemicals Ropes made of other synthetic fibers such as Dacron, polyethylene, and polypropylene have char acteristics that make them very good per formers in certain applications In a lifeline where shock loading strength and high energy absorption is paramount, nylon is superior Knots reduce the strength of all ropes (See Table 26-C ) Tests have shown that mamla lifelines of 3-in diameter, when knotted around a bar or other anchorage, are not strong enough at the knots to be safe for gen eral use unless a shock absorber of low load limit is used How much a knot reduces strength depends upon the type of knot or hitch used and the amount of moisture in the rope Moisture increases the strength of a rope in a knot or around a sharp bend, and dryness greatly diminishes its strength at such points In some cases, a knot will reduce the tensile strength of a rope to less than half of its breaking strength If rope is spliced mto snaps and D-nngs instead of knotted (Fig 19-42), the splice will retain approximately 90 percent of the breaking strength of the rope Breaking strength is always measured m a straight line pull on the rope (See Chapter 26, "Ropes, Chains, and Slings ") Manila rope of &-in diameter has a break ing strength of approximately 2650 pounds, or (dividing by a safety factor of 5) a safe load strength of 530 pounds Spun nylon rope of %nn diameter is rated to have a breaking strength of 6400 pounds--a safe load strength of 710 pounds Manila rope of X-m diameter rates a break ing strength of 5400 pounds--a safe load strength of 1080 pounds When a low-loadlimit shock absorber is used, X-in mamla rope or X-in nylon rope is considered strong enough for most lifelines Without a shock absorber, even X-in mamla rope may not be strong enough to stop a long fall If no shock absorber is available, X-in nylon rope is usually preferable to mamla rope for impact use, because it stretches more and will act as a partial shock absorber The chief disadvantage of nylon for this use is that much of its stretch occurs at a very low load ing, thus the falling workman can fall a con siderable distance closer to some possibly damaging obstruction before an adequate stopping force is exerted by the rope Thereafter, the loading increases very rap idly to a rather high foice before the final stop Also, a considerable amount of re bound is obtained from nylon at the higher loadings Wire ropes should not be used as lifelines wheie a free fall is possible unless some shock-absorbing device is also used, because their rigidity greatly magnifies the impact loading Wire ropes are hazardous when used around electricity Lifelines should be bed to permit as little slack as possible, and thus stop a man with the minimum free fall Special notice must be taken of the nearness of any beam or other obstruebon which the workman might sbike in case of a fall Serious injury or death may result if the total free fall plus the total stretch or elongation of the lifeline and shock ab sorber will allow the workman to sbike some damaging object before he is stopped If there is a long clear space m which a man may be stopped, then a low-limit shock ab sorber may be used with less discomfort to the workman If this space is closely limited, a shorter stop is imperative, even though greater discomfort results Wire lopes should be kept clean and dry and should be frequently lubricated Before 513