Class 1: Air with low contaminant concentration, low sensory-irritation intensity, and inoffensive odor.<br>Class 2: Air with moderate contaminant concentration, mild sensory-irritation intensity, or mildly offensive odors. Class 2 air also includes air that is not necessarily harmful or objectionable but that is inappropriate for transfer or recirculation to spaces used for different purposes.<br>Class 3: Air with significant contaminant concentration,significant sensory-irritation intensity, or offensive odor.<br>Class 4: Air with highly objectionable fumes or gases or with potentially dangerous particles, bioaerosols, or gases, at concentrations high enough to be considered harmful
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