Some of the risks or hazards involved in working in confined spaces can be broadly classified as atmospheric, engulfment, entrapment, mechanical and electrical categories. Atmospheric hazards include little or too much oxygen, flammable gas, or combustion dust. Engulfment hazards include being swallowed in sand or grain; entrapment hazards include suffocation or entrapment by inwardly converging walls, or sloping floors. Mechanical hazards include conveyors or gears. Other risks that an entrant may encounter include poor lighting, unsecure footing, falling objects, temperature extremes and more.