Which statement about Physical Heat Exposure Limit (PHEL) curves is true?

• A. Navy uses 4 curves
• B. Navy uses 5 curves
• C. Navy uses 6 curves
• D. Navy uses 7 curves

Answer: (C)

PHEL curves show how long you can be exposed to a heat source before reaching a safe limit, depending on how intense the heat is and what clothing or protective gear you’re wearing. The Navy uses six curves because naval work spans a range of heat conditions and protection levels, and each curve matches a different combination of heat load and gear. This allows you to select the curve that best fits the actual scenario—providing a clearer, safer guideline than a single curve and without adding unnecessary complexity. If there were too few curves, some conditions wouldn’t be represented accurately; adding more than six isn’t standard practice in this material.