Many legislations around the world stipulate that supplied air equipment must be used in all areas that can be described as confined space.

Common examples of confined space include tanks, cisterns, reservoirs, silos and other storage facilities, but many other places can also belong to this category.

Whether supplied airline equipment or self-contained breathing apparatus should be used depends on the type of work and on local legislations.

When working in a confined space, at least one person should always be outside the work are. This person must be in constant contact with the worker inside the confined area. A harness or life line should always be worn, and the person outside must be strong enough to pull or lift the worker out of the confined space in case of an emergency.

Many legislations demand that supplied air equipment be used if the concentration of the respiratory hazard is greater than 100 times its exposure limit (in most cases, a half mask with filter is considered adequate up to 10 x exposure limit. At concentrations between 10 and 100 times the limit, a full face mask with filter can be used).

If the atmosphere contains IDLH materials (Immediately Dangerous to Life and Health), only breathing apparatus must be used in most countries.

If there is less than about 19% oxygen in the air (check local regulations), supplied air is the only solution, either as airline respirators or as self-contained breathing apparatus.

Remember that oxygen deficiency can occur even in an open area, such as a room or even a depression in the ground. If the hazard is heavier than air, it can gather in the room or in the hollow, pushing the air (and thus oxygen) away.

Depending on local laws, filter respirators may be prohibited for work with certain chemicals. For instance, in many places, spray painting with two-pack paint (toluene di-idocyanate) can only be done with supplied airline equipment.