What is the correct order of the three most common atmospheric tests?

• A. Oxygen, 2. Combustible/Flammability, 3. Toxins
• B. Toxins, 2. Oxygen, 3. Combustible/Flammability
• C. Combustible/Flammability, 2. Toxins, 3. Oxygen
• D. Oxygen, 2. Toxins, 3. Combustible/Flammability

Answer: (A)

Assessing atmospheric hazards in order of immediate risk: breathable air first, then explosion risk, then toxic exposure. The air must be breathable before anyone can safely work, so checking oxygen levels comes first. If oxygen is deficient or enriched beyond safe limits, entry decisions can’t proceed safely regardless of other hazards. Next, evaluate for flammable or combustible gases. A presence of flammable vapors creates a serious ignition/explosion hazard, so knowing the flammability level guides ventilation, ignition-control measures, and entry procedures. Only after confirming adequate oxygen and the absence (or control) of flammable atmospheres should toxic contaminants be assessed, since toxic exposure adds health risk that requires its own protective strategies and time considerations. This sequence—oxygen, then combustible/flammability, then toxins—best reflects the priority of life-safety hazards before chemical exposure hazards.