Plain English:
502.1 general: Provide, maintain, and run exhaust anywhere equipment or processes throw off dust, light particles, heat, odors, fumes, spray, gas, or smoke in amounts that can irritate or impact health/safety.
502.1.1 exhaust location: Put exhaust inlets where contaminants are heaviest, not just where the duct route is convenient.
502.1.2 fuel-dispensing: In fuel-dispensing areas, the bottom of exhaust or inlet openings must be <=18 in above the floor to capture heavy flammable vapors.
502.1.3 equipment/service rooms: Rooms with odor, fume, gas, steam, dust, or spray sources must be built and exhausted so contaminants do not spread to other occupied spaces.
502.1.4 hazardous exhaust: Exhaust with high concentrations of dust or hazardous vapors must meet IMC 509 hazardous exhaust requirements.
502.2 aircraft fueling/defueling: Compartments with fueling piping, pumps, separators, hose reels, etc. must be ventilated at floor level or within the floor to pick up fuel vapors.
On Plans: Why it matters
502.1 is a catch-all trigger: if a process makes bad air, you likely owe exhaust, even if the room name looks "normal."
High, ceiling-only grilles in fuel or heavy-vapor zones miss the layer where vapors actually sit.
Treating hazardous exhaust like normal environmental air can break IMC 509 and IFC requirements.
Code Path: Where to show it
M-001: IMC 502 note listing general exhaust triggers and "PROVIDE HAZARDOUS EXHAUST PER IMC 509 WHERE APPLICABLE."
M-101: Exhaust inlets tagged with location (for example, "LOW EXH INLET <=18 IN AFF" at fuel-dispensing; "HIGH EXH INLET" for light/hot vapors).
M-601 schedules: Exhaust schedule with columns for EXHAUST TYPE (environmental / hazardous / fuel-vapor) and CODE REF (502.1, 502.1.2, 502.1.4, 502.2).
Check: Do
Ask what each space actually does (charging, mixing, fueling, cleaning, spraying) and check it against 502.1.
Match inlet elevation to the contaminant: low for heavy vapors, high for light/hot vapors.
Flag any "hazardous exhaust" and run it through a Section 509 check (duct construction, routing, terminations).
Review Risk: Don't
Rely only on Chapter 4 room names and miss process-driven 502 triggers.
Use a single high ceiling grille in fuel-dispensing or aircraft fueling areas and ignore the 18 in rule.
Combine hazardous exhaust with environmental exhaust or return systems.
Field Tip:
On M-001, add a small "IMC 502 REQUIRED EXHAUST" note or schedule listing: ROOM / PROCESS / EXHAUST TYPE / CODE SECTION / DESIGN BASIS (CFM, ACH, or velocity). It shows reviewers you evaluated the process, not just the room name.
Masterbuild QA Lens
Product-conveying system design starts with the contaminant source classification: explosive, flammable, combustible, corrosive, or health-hazard material. The classification determines duct material, separation requirements, and discharge location. Confirm the classification is stated on M-001 before any duct material or termination location is selected.
Drawing / Submittal Check
For general exhaust systems (502.1-502.2): the drawings must show the exhaust rate for each space, the exhaust system serving the space, the makeup air path (door transfer, dedicated duct, or building pressurization), and the exhaust outlet and intake locations. Missing makeup air path is the most common 502 general-exhaust comment - every exhausted space needs its makeup path shown, even when it is just an undercut door.
Common Review Risk
The most common general exhaust risk is an exhaust rate lifted from the general ventilation table instead of the required-exhaust table for the specific space, paired with a fan schedule that cannot deliver the tabulated rate at the actual duct static. Verify the rate source and the fan curve together.
When To Escalate
Escalate when the general exhaust system must serve multiple occupancy types with different required rates on the same air-handling unit. VAV exhaust systems that must maintain different minimum rates in different zones require controls coordination that goes beyond standard exhaust design. Get the controls engineer involved before the permit set is issued.
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.
Special Exhaust Coordination
For specialty exhaust, start with the contaminant and source. Then confirm capture method, duct material, routing, discharge, separation, controls, and whether another consultant or AHJ review is required.