What Are Explosion-Proof Units?

Explosion-proof exit signs, emergency lights, and combo units are sealed, spark-containing fixtures engineered so any internal arc, heat, or flame is contained within the housing, preventing ignition of surrounding gases, vapors, dusts, or fibers.

Models are typically evaluated to UL 924 (egress performance) and, in hazardous areas, UL 844 (hazardous-location construction). Match Class/Division/Group to the space: Class I (gases/vapors), Class II (dusts), Class III (fibers); Division 1 = likely/continuous, Division 2 = abnormal.

Use Cases

• Oil & Gas: Refineries, terminals, offshore platforms, tank farms.
• Chemical Processing: Solvent handling, coatings, battery plants.
• Food & Grain: Mills, silos, conveyors — combustible dust.
• Wastewater: Digesters, pump rooms — methane exposure.
• Paint/Finishing: Spray booths, mixing rooms, curing lines.

⭐ Highlight: Combos mark exits and light the path in one rugged device — fewer penetrations into classified spaces and simplified maintenance.

Compliance: Codes & Ratings

• UL 924 — Verifies emergency illumination, battery transfer, and 90-minute runtime.
• UL 844 — Construction for hazardous locations (Class/Division/Group + T-code).
• NFPA 101 — Life Safety Code; reliable egress lighting and EXIT visibility.
• OSHA 1910.37/38 — Safe egress routes and clearly marked exits.
• NEC 500–516 — Classification, equipment selection, and wiring methods.

Verify that the unit is listed to the applicable standards for both functions—UL 924 for emergency egress performance (incl. 90-minute runtime) and UL 844 for hazardous-location construction (Class/Division/Group + T-code). Most explosion-proof products carry both where required; always confirm on the datasheet for your AHJ.

Testing & Maintenance

• Monthly: 30-second functional test (manual push-to-test or self-diagnostics).
• Annually: 90-minute full discharge to validate battery capacity and optics.
• Logs: Document pass/fail and corrective actions; AHJ may request records.

Self-testing models cut labor by automating routine checks and flagging battery faults or LED failures. Still, perform visual inspections for corrosion, gasket integrity, and lens cleanliness. In tall bays, planning circuit groups for testing windows minimizes lift time and operational disruption.

Further reading: Maintaining Explosion-Proof Exit Signs & Emergency Lights

Key Features to Compare

• Listings: UL 924 & UL 844 (correct Class/Division/Group + T-code)
• Optics: High-efficacy LEDs; aimable heads; uniform beam
• Enclosure: NEMA 4X / IP66; marine-grade or powder-coat finish
• Power: 90-min battery; optional cold-weather kit; 120/277 V
• Diagnostics: Self-testing & status LEDs; remote test option
• Mounting: Wall/ceiling/pendant hardware; conduit hubs; hinge-access

Further reading: Installing Explosion-Proof Emergency Lighting: Step-by-Step

Price Range & Cost Considerations

Explosion-proof combos cost more than standard hazardous-location emergency lights because flame-path geometry, gasketing, and certification add engineering and test overhead. Typical ranges:

• Class I Div 2 (baseline): $850–$950 — core features, rugged housing, UL listings
• Mid-tier (with diagnostics): $1,000–$1,200 — self-testing, enhanced optics, NEMA 4X
• Div 1 / specialty: $1,400+ — heavier castings, higher T-code margins

A combo can replace two or three separate fixtures (exit sign + emergency heads), reducing penetrations into classified spaces, conduit runs, and maintenance points. Over the life of the system, that consolidation can offset initial spend — especially when factoring lift time for annual testing and battery replacements.

Combo vs Separate Fixtures

Here’s how the two approaches compare in hazardous areas:

Combo Units

• Single device satisfies EXIT visibility and egress illumination
• Fewer enclosures and penetrations in hazardous areas
• Ideal at doorways, corridor junctions, and compact egress zones

Separate Fixtures

• Flexible aiming for high-bay or large-area photometrics
• Scalable lumen packages using dedicated hazardous-location emergency lights
• Useful when exit signs and lights need independent placement

Many facilities deploy a hybrid layout: explosion-proof combos above doors for wayfinding plus separate hazardous-location emergency lights to bolster foot-candles across wide process floors. In small rooms or corridors, a 2-in-1 explosion-proof exit sign is often the most cost-effective approach — one device to install, test, and service.

Further reading: Combos vs Separate in Hazardous Areas

Conclusion

Explosion-proof combo units deliver two critical life-safety functions in one sealed, code-listed device. Select the correct Class/Division/Group, verify UL 924 / UL 844, match T-code and NEMA/IP to the environment, and maintain monthly/annual tests with a clear log. Whether you standardize on all-in-one explosion-proof exit signs or mix combos with separate heads for large areas, the goal is the same: reliable egress visibility without ignition risk.

See also: AHJ Inspections in Hazardous Areas — What Inspectors Check