Locate the source of supplied air, whether it is an air compressor or an ambient air pump, such as a Bullard Free-Air pump, in a clean air environment. Locate the air source far enough from your work site to ensure the air remains contaminant-free. Always use an inlet filter on the air source. Use suitable filters and carbon monoxide monitors and alarms, like Bullard’s CAB Series of CO monitors, as necessary to assure clean, breathable air at all times. The air should be regularly sampled to be sure that it meets Grade D requirements.