Cartridges should be replaced regularly with heavy use, or the carbon's capacity will be exhausted and contaminants will pass through the filter and be inhaled. In some instances the wearer may detect odor as the cartridge becomes loaded. For protection during spray painting or pesticide application, chemical cartridges that work in conjunction with a specific mechanical filter should be used. The powered air purifier can be a mechanical filter, or chemical cartridge respirator, or a combination of both. These devices have a motor blower assembly that forces air through the filter and into the breathing zone of the wearer.
Breathing is much easier because no effort is required to draw air through the filter.
Powered air purifiers may be preferred for excessively high concentrations of dusts or pesticides, but they cannot be used in oxygen-limited environments. Common headgear for powered air purifiers consists of a hard helmet and a rigid visor. Non-rigid head and face covers also are available. Powered air purifiers are powered by a battery pack strapped onto the user's waist or back. The batteries may be of the rechargeable or disposable type.