What substances must be kept away from cylinders, valves, and apparatus?

The correct response identifies oily and greasy substances as those that must be kept away from cylinders, valves, and apparatus. This stems from the understanding that when working with gases, particularly flammable or combustible gases, the presence of oils and greases can pose significant hazards. These substances can ignite easily and create dangerous situations, especially when they come into contact with the high-pressure gases within the cylinders.

Furthermore, oily residues can compromise the integrity of the valves and seals, leading to leaks or failures that could result in catastrophic outcomes. Ensuring that all equipment is free from such contaminants is vital for maintaining safety protocols in welding and cutting practices.

While keeping dust and dirt, water, and plastic materials away from these areas is also essential—primarily for maintaining equipment performance and safety—oily and greasy substances present a greater and more immediate risk, making them the more critical focus in this context.