The employer (user) must first assemble the necessary toxicology, safety, and other relative environmental information for each respiratory hazard in the workplace to include the following:

- General use conditions, including determination of all contaminants.

- Physical, chemical, and toxicology properties of those contaminants.

- NIOSH recommended exposure limits (REL), OSHA permissible exposure limits (PEL), American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLV), State-OSHA exposure limits, American Industrial Hygiene Association (AIHA) Workplace Environmental Exposure Limit (WEEL), or other applicable occupational exposure limit.

- Expected concentrations of each respiratory hazard.

- Immediate dangerous to life or health (IDLH) concentrations.

- Oxygen concentration or expected oxygen concentration.

- Eye irritation potential.

- Other environmental factors, such as the presence of oil aerosols.

NIOSH recommends that air sampling be conducted to determine exposure levels found in the workplace.  A combination of air sampling and exposure modeling is often used to make reasonable estimates of exposure.  Ideally, this determination should be made by a professional industrial hygienist. Also, OSHA offers free consultations to qualifying small and medium-sized businesses to help identify problems and suggest approaches to correct those problems found.  OSHA also provides assistance to these businesses by supplying them with a list of potential support resources that might be available to assist them in correcting specific problems. The OSHA website (www.osha.gov) provides information on compliance assistance and consultation programs.

The information obtained on general use conditions for respirators should include a description of the actual job being performed, including job task, duration and frequency, location, physical demands, industrial processes, as well as issues affecting the comfort of the respirators. Some conditions may preclude the use of specific types of respirators in certain circumstances because the individual must medically and psychologically suited (i.e., not claustrophobic) to wear a given respirator for a given task, particularly if the respirator is a self-contained breathing apparatus (SCBA).