Final answer:
Employers must test for atmospheric hazards by checking first for oxygen, followed by combustible gases and vapors, and finally for toxic gases and vapors, in compliance with safety standards.
Step-by-step explanation:
When testing for atmospheric hazards, employers are required to test first for oxygen, then for combustible gases and vapors, and then for toxic gases and vapors. The correct sequence is: 1) oxygen, 2) combustible gases and vapors, and 3) toxic gases and vapors. This requirement ensures that environments are first verified for adequate oxygen levels, which are necessary for survival. Subsequently, the presence of potentially explosive or flammable hazards is checked.
Lastly, the assessment of the air quality includes testing for toxic substances, which could pose health risks upon inhalation. Each type of hazard requires specific measures to mitigate risk and is crucial for maintaining a safe workplace in accordance with OSHA standards.