Because external combustion engines are relatively inefficient in their use of fuel, the exhaust also spews live embers and sparks, which have caused grass or forest fires near the right-of-ways—smokestacks must be capped with spark arresters which trap the larger, more dangerous particles. Some mountain locomotives were equipped with spark arresters using long tubes to deposit cooled embers in hoppers mounted on the boiler Modern photos of D&SNG locomotives show the stacks topped with "bear-trap" spark arresters.