ANSWER: Various items need to be considered when choosing the appropriate respirator. If the exposure level is less than 10 times the exposure limit, usually some type of half-mask respirator can be chosen. Instances in which this may not be true include areas in which the contaminant is unknown, the atmosphere is immediately dangerous to life or health, a substance-specific standard specifies otherwise, or some other factor dictates a higher level of protection. The proper choice should be made with the help of a qualified health and safety professional, such as an industrial hygienist. NIOSH is the regulatory agency that governs the certification and manufacture of respirators. NIOSH certifies three series: N, R and P with three levels of filter efficiency - 95 percent, 99 percent and 100 percent (actually 99.97 percent). Once a product has been approved by NIOSH, it receives a TC number that shows it is certified.
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