Marking Hazardous (Classified) Locations is a critical step in both compliance and personnel safety. While OSHA and the NEC (NFPA 70) mandate the classification of these areas, they are surprisingly quiet on exactly how to physically mark them.
Because “invisible” hazards like flammable vapors or combustible dust can’t be seen, you should use a tiered approach to ensure anyone approaching the area knows the risks. Members can download my written program for “Demarcating HAZLOCs” at the end of this article.
- Visual Floor Markings
Using floor tape or paint is the most effective way to define the physical boundaries of a Class I or Class II location.
Color Standard: Use Red/White or Black/Yellow diagonal "hazard" stripes.
The Perimeter: Apply the marking at the exact boundary where the classification ends (e.g., the 10-foot radius from an open sump).
Text Overlays: Use "stenciled" floor markings that explicitly state: "HAZARDOUS AREA - NO SMOKING" or "CLASSIFIED AREA - PERMIT REQUIRED."Signage at Entry Points
Every point of ingress to a classified area should have high-visibility signage. According to ANSI Z535 standards, these should include:
Header: DANGER or WARNING.
The Hazard: Clearly identify the nature of the hazard (e.g., "Flammable Vapors Present" or "Combustible Dust Hazard").
Prohibitions: Explicitly list forbidden items, such as:
No Smoking or Open Flames.
No Unrated Electronic Devices (Cell phones, cameras).
No Spark-Producing Tools.Equipment Labeling
Individual pieces of equipment within the area should also be marked to prevent maintenance errors.
ID Tags: Mark junction boxes and conduits with the specific classification (e.g., "Class I, Div 1, Group D").
Intrinsic Safety: Clearly label intrinsically safe (IS) wiring and barriers—typically using light blue labels or tape—to ensure they aren't cross-wired with non-IS circuits.Documentation & Mapping
Physical markings can wear out. Maintain a “Master Hazardous Location Plan” (also known as a Hazardous Area Classification Drawing).
Post the Map: Display a laminated copy of the area map at the entrance to the facility or the specific process unit.
Update Regularly: Ensure markings are refreshed after any process changes or equipment moves that might alter the "envelope" of the classified area.Best Practice Tip: The “Ignition Source” Audit
When you mark these areas, it is a great time to audit for “stealth” ignition sources. Check that all temporary lighting, heaters, and even the janitorial staff’s vacuum cleaners are appropriately rated for the zone you just marked.
Safety Reminder: If you are marking a Class II (Dust) area, remember that the "boundary" can shift based on housekeeping. A heavy layer of dust outside your marked zone effectively extends the hazardous area.