/ Field knowledge · IMC 502.7
If the spray gun still runs when the fan is off, it is not 502.7.
Spray exhaust is not a box fan in the window. IMC 502.7: provide exhaust wherever flammable finishes are sprayed or applied — including during construction. Run it during and after spraying so vapors clear. Interlock the spray equipment so it cannot run unless the exhaust is on. Spray exhaust is normally not recirculated. Any recirculation must keep vapors below 25% of the lower flammable limit (LFL) with monitoring and automatic shutdown. Each booth or room gets its own exhaust to outdoors unless the manifold rules are actually met.
Educational 2024 International Mechanical Code (IMC) 502.7–502.7.7 from Daily Code Talk. Confirm the adopted edition. Distinct from 502.12 enclosed coating (1 cfm/ft² at the floor) and 503 spark-resistant fans. This is not a spray-booth design.
- 502.7: exhaust wherever flammable finishes are sprayed or applied, including during construction.
- 502.7.3: run during and after spraying. Interlock so spray cannot run without exhaust. Recirculation is the exception, not the default — below 25% LFL, with monitoring and auto shutdown.
- 502.7.3.5–502.7.7: each booth/room its own exhaust to outdoors unless the strict manifold conditions are documented. Non-sparking fan wheels. Motors out of the airstream. Dipping, electrostatic, powder, and floor-resurfacing operations keep vapors well below hazardous levels.
- Do not manifold spray exhaust into house return. Do not leave the interlock as “by others.”
On the set: show the booth as its own exhaust to outdoors, the interlock (spray dead if the fan is dead), fan construction (non-sparking, motor out of the airstream), and that recirculation is either not claimed or meets the 25% LFL + monitor + shutdown path. 503 still governs the fan hardware.
A spray booth that recirculates with no LFL monitor
Or spray equipment that still runs when the fan is off. Or three booths on one environmental exhaust riser. Those are the redlines. Type II dry-cleaning rooms are a different 502.6 row (1 cfm/ft²) — process first, then the fan.
Source: Daily Code Talk — IMC 502.2–502.7 · tool: Interlock / recirc screen · coating: 502.12 · fans: 503 · 509: hazardous exhaust.
What to send
Whether this is a booth, a room, or “spray in the bay,” whether the gun is interlocked with the fan, and whether air returns to the shop or goes outdoors.
If the spray gun still runs when the fan is off
Send the booth cut and the control note. Masterbuild will say whether 502.7 still has no interlock — or 502.7 still recirculates with no LFL monitor.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. Interlock, no default recirculation, 25% LFL with monitoring, dedicated outdoor exhaust, non-sparking wheels, and motors out of the airstream are 2024 IMC 502.7 education from Daily Code Talk — not a spray-booth design. This page is not legal advice.