Plain English:
502.1 general: If a process makes "bad air" (dust, fumes, heat, vapors, spray, smoke) that can irritate or affect health/safety, IMC 502 says you owe exhaust-even if Table 403 doesn't name the room.
502.2-502.7 special processes: Aircraft fueling, battery charging/rooms, dry cleaning, flammable finishes, spray booths, dipping, electrostatic, powder coating, and floor resurfacing all get specific exhaust rates (cfm/ft^2, face velocity) and "run while the process runs" rules.
502.8 hazmat: Over maximum allowable quantities (MAQ), storage and use areas need hazmat exhaust (often >=1 cfm/ft^2, usually continuous), emergency shutoff, pickup height based on vapor density, and no recirculation of contaminated air to occupied spaces.
502.9 specific materials: Adds extra rules for medical gases, corrosives, cryogenics, flammable/combustible liquids, highly toxic/toxic liquids and gases, ozone, LP-gas, silane, etc. Think local capture at the source, 200 fpm at gas cabinet/enclosure faces, and scrubbers where leaks or spills can create dangerous vapors.
502.10 HPM + 502.11-502.20 special occupancies: HPM fabs, gas rooms, gas cabinets, projector rooms, organic coating rooms, garages/pits, gaseous-fuel repair, tire recapping, firing ranges, and mani/pedi stations all need purpose-built exhaust with defined rates, pickup locations (low/high/local), and sometimes interlocks.
On Plans: Why it matters
IMC 502 is where "normal" exhaust stops and special/hazardous exhaust begins. Missing MAQs, process exhaust, or treatment plans is a common plan-review stall.
Code Path: Where to show it
M-001: "IMC 502 REQUIRED EXHAUST" note listing key triggers (process rooms, hazmat, HPM, special occupancies) and that design is based on cfm/ft^2, cfm/lamp, or face velocity as applicable.
M-101: Tag special and hazmat/HPM rooms and show LOW / HIGH / LOCAL pickup or source capture.
M-601: "IMC 502 REQUIRED EXHAUST" schedule with ROOM, PROCESS, EXHAUST TYPE, DESIGN BASIS, and CODE REF.
Check: Do
Ask what actually happens in each room and check it against IMC 502.
Coordinate early with architect and fire protection on MAQs, NFPA 704 ratings, room ratings, and shafts so IMC/IBC/IFC all tell the same story.
Review Risk: Don't
Recirculate exhaust from spray, flammable finish, hazmat, HPM, or firing range systems unless every code condition is clearly met and documented.
Combine these exhaust streams with general return or environmental exhaust.
Field Tip:
Build a "IMC 502 REQUIRED EXHAUST" schedule block in your template so every project has a one-glance list of special, hazmat, and HPM exhaust-even when the answer is "NONE." It proves you actually ran the 502 checklist.
Masterbuild QA Lens
Before submitting any 502 exhaust design: (1) confirm the contaminant source classification drives the section reference; (2) verify makeup air intent - negative pressure exhaust-only zones need a documented makeup path; (3) confirm all ducts classified as product-conveying meet Chapter 6 material requirements for the classification.
Drawing / Submittal Check
The summary sheet should include a required exhaust matrix: each space or system type, the governing IMC 502 subsection, the required exhaust rate, the makeup air provision, and any special requirements (standby, alarming, fire rating). A completed matrix survives plan review faster than systems scattered across multiple sheets with no consolidated reference.
Common Review Risk
Required exhaust matrix errors discovered during inspection - a space that was in the occupancy drawings but not in the exhaust design - require an amendment. The inspection finds the space, the inspector checks the permit set, the space is not covered, and work stops. An exhausted-space inventory verified against the architectural occupancy drawings before submittal prevents this.
When To Escalate
Escalate when the required exhaust matrix reveals a gap between the building code occupancy classification and the fire code occupancy classification - when the two do not agree on what exhaust system is required. These disagreements are resolved at the pre-application meeting, not during plan review.
Special Condition-Battery Rooms
For battery rooms or charging areas, confirm the battery type, hazard basis, ventilation calculation, control sequence, alarm interface, exhaust path, and AHJ or fire-protection coordination are all traceable. The drawing set should not leave the safety logic implied.
Rated Assembly Coordination
Required exhaust systems for occupancies like bathrooms, kitchens, and parking garages all cross rated assemblies at some point. The coordination checklist should map every exhaust duct to the assembly it crosses and the damper or firestop required.