1. Level A. The chemical substance has been identified and requires the highest level of protection for skin, eyes, and the respiratory system based on either:

A. Measured or potential for high concentrations of atmospheric vapors, gases, or particulates.

B. Site operations and work functions involving a high potential for splash, immersion, or exposure to unexpected vapors, gases, or particulates of materials that are harmful to skin or capable of being absorbed through intact skin.

C. Substances with a high degree of hazard to the skin are known or suspected to be present and skin contact is possible.

D. Operations are conducted in confined, poorly ventilated areas.

II. Level B. The type and atmospheric concentrations of substances have been identified and require a high level of respiratory protection, but less skin protection than that of an A site. This involves atmospheres:

A. With IDLH concentrations of specific substances that do not represent a severe skin hazard.

B. That do not meet the criteria for use of air-purifying respirators.

C. Containing less than 19.5 or greater than 23.5 per- cent oxygen.

D. When incompletely identified vapors or gases are indicated by direct reading organic vapor detection instruments, but vapors and gases are not suspected of containing high levels of chemicals harmful to skin or capable of being absorbed through the intact skin.

NOTE: If the preliminary site evaluation does not produce sufficient information to identify the hazards or suspected hazards (i.e., unknown atmosphere), an ensemble providing protection equivalent to Level B PPE shall be provided as minimum protection, and direct reading instruments shall be used, as appropriate, for identifying IDLH conditions.

III. Level C. The atmospheric contaminants, liquid splashes, or other direct contact will not adversely affect any exposed skin.

A. The types of air contaminants have been identified, concentrations have been measured, and air purifying respirators are available to effectively remove the contaminants.

B. All criteria for the use of air purifying respirators are met.

IV. Level D The atmosphere contains no known hazard. Work functions preclude splashes, immersion, or the potential for unexpected inhalation of or contact with hazardous chemicals.