When referring to the US military marking system, if a circle with a symbol of a person wearing a mask is seen, it is necessary to assume that:

• A. A protective mask or breathing apparatus must be used
• B. Only gloves are required
• C. No protective equipment is needed
• D. A warning if smelled

Answer: (A)

That symbol signals an airborne hazard and requires respiratory protection before entering the area. In the US military marking system, a circle showing a person wearing a mask means you must use a protective mask or breathing apparatus, because the danger is inhalation and gloves or eye protection alone won’t keep you safe. You can’t rely on smell to detect these hazards—many toxic substances are odorless or masking agents can dull your sense of smell—so assuming you need a respirator is the correct precaution. If you’re unsure of the agent involved, treat it as a respiratory risk and deploy the appropriate respirator and PPE as indicated by procedures and safety data.