What must be known in order to wear an Air Purifying Respirator (APR)?

To properly wear an Air Purifying Respirator (APR), it is essential to understand the chemical concentration, the percentage of oxygen in the environment, and the specific hazards associated with the chemical in question.

Understanding chemical concentration is crucial because it directly influences whether an APR can provide adequate protection. Each APR is rated for specific concentration levels of various substances. If the concentration exceeds the respirator's capabilities, the user may be exposed to harmful levels of contaminants.

Knowing the oxygen percentage in the atmosphere is also vital. APRs rely on the ambient air for filtering out contaminants; therefore, if the oxygen level is below a safe threshold, the APR will not function effectively, and alternative respiratory protection must be utilized.

Additionally, being aware of the specific hazards allows the user to select the appropriate respirator model designed for the types of chemicals or particulates present, ensuring effective filtration of harmful substances.

While the other options present relevant factors, they do not encompass the essential requirements as thoroughly. For instance, chemical type, vapor pressure, and toxicity might influence APR selection, but they do not address the critical factor of oxygen levels and how that relates to air quality.