Manhole covers are generally made of steel and are quite heavy. In fact each year many American Utility Workers are injured due to the heavy covers. Fingers are crushed, heads banged and backs sent out of alignment. Today some cities have gone to replacing the manhole covers with synthetic or composite covers which can take the same amount of weight without cracking, do not rust, weigh considerably less and are not stolen to turn in for scrap metal. Some larger cities lose some 100-300 manhole c.