Inspection · Hazloc Labs

Area Classification vs DHA: How the Two Studies Connect

Facilities often commission a DHA and an area classification package as if they were the same deliverable. They are linked — but they answer different questions.

Different questions

Study	Primary question	Typical output
DHA (NFPA 652)	Where can dust explode/fire, and what safeguards are needed?	Hazard scenarios, safeguards, recommendations
Area classification	Where must electrical equipment be suitable for an explosive atmosphere?	Zone/Division drawings & basis

How they should connect

1. DHA identifies credible dust clouds/layers and ignition scenarios.
2. Classification translates atmospheric likelihood/extent into electrical zones/divisions.
3. Electrical design selects Ex / Division equipment and wiring methods from those drawings.
4. Housekeeping and ventilation assumptions in the DHA must match classification basis notes — or drawings lie.

Handoff checklist for electrical teams

• Revision-controlled drawings with zone/division legends
• Material explosibility data used (Kst, MIE, MIT/LIT) with test IDs
• Basis of safety notes (ventilation, containment, housekeeping limits)
• Hybrid gas+dust areas flagged explicitly

FAQ

Can we classify without a DHA?

For combustible dust, NFPA 652 expects DHA. Classification without a defensible dust hazard basis is a common audit finding.

Does gas classification need a DHA?

Gas/vapor classification uses different methods (e.g. NFPA 497 / IEC 60079-10-1). Still document the release basis.

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