Refs: [FG] IMC 304.5, 304.5.1-304.5.3; IMC 502.16; IMC 202
Plain English:
[FG] 304.5 (General): Install/location per listing + MI. Hydrogen spaces in public/private/repair/parking garages & fuel-dispensing facilities require ventilation by 304.5.1, 304.5.2, or 304.5.3. Rooms that communicate directly with a private garage are treated as the garage.
[FG] 304.5.1 (Natural ventilation): Room <= 850 sf; provide two permanent openings in the same exterior wall: upper within 12 in of ceiling, lower within 12 in of floor. Total free area >= 0.5 sf per 1,000 cf of room volume; min opening dimension 3 in; ducts (if used) same area as openings. Ignition sources >= 12 in below ceiling. H₂ output limit: <= 4 scfm per 250 sf of floor area.
[FG] 304.5.1.2 (Louvers): Use net free area; if unknown: wood = 25%, metal = 75%; louvers fixed open.
[FG] 304.5.2 (Mechanical ventilation): Ventilate per IMC 502.16; place ignition sources below exhaust outlet elevation.
[FG] 304.5.3 (Engineered alternative): Approved engineered system may replace 304.5.1/304.5.2.
On Plans: Why It Matters
Hydrogen is lighter-than-air and accumulates near the ceiling. The code forces either ceiling-level relief (natural), engineered exhaust (mechanical), or a sealed design basis (engineered) - plus listing/MI-to prevent ignition at the stratification layer. Miss the sizing or placement -> expect holds, redesign, and re-inspection.
🧾 Where To Show It (sheet map)
M-001: "Hydrogen installs per 304.5; select natural (304.5.1), mechanical (502.16), or engineered (304.5.3). Rooms communicating with private garages are garage. Show ignition-source placement rules."
M-101/...: Delineate hydrogen room envelope, tag opening locations/heights or exhaust outlet heights, show direct communication to garages.
M-501/502: Details: two-opening natural vent (upper/lower), mechanical exhaust layout with outlet elevation, and engineered narrative callout.
M-601: Vent Path (Natural/Mech/Eng), Room Area (sf), Volume (cf), A_free (sf), Upper/Lower Opening Net/Gross (sf), Louver factor, Exhaust cfm & outlet elev (mech), Ignition-source elevation.
Code Path: Hydrogen System Documentation
M-001 must identify the hydrogen system type (generating or refueling), quantity and storage location, ventilation rate for storage and dispensing areas, and electrical classification zone.
M-101 must show the hydrogen room envelope with opening locations (upper and lower for natural ventilation) or exhaust outlet locations for mechanical ventilation.
M-601 must include: vent path (natural/mechanical/engineered), room area and volume, free area of openings or exhaust cfm, and detection/alarm sensor type and location.
Check: Hydrogen Ventilation Documentation
Confirm the ventilation method is explicitly chosen (natural 304.5.1, mechanical 502.16, or engineered 304.5.3) and documented on M-001.
For natural ventilation: confirm two permanent openings (upper opening near ceiling, lower opening near floor) with opening areas calculated on the schedule.
For mechanical ventilation: confirm exhaust per IMC 502.16 with ignition sources located away from exhaust outlets per 304.5.2.
Review Risk:
Hydrogen system permits require fire marshal pre-review in most jurisdictions - submitting to the building department without prior fire marshal coordination adds significant time to the permit path.
Electrical classification zone not shown on the electrical and mechanical drawings is a common hydrogen permit comment.
Missing detection and alarm documentation (sensor type, setpoints, alarm connection) is a routine fire marshal review flag.
Masterbuild QA Lens
Seismic requirements under 304.5.1-304.5.3.1 are often passed to structural with a note - but the mechanical team is still responsible for confirming the anchorage meets the IBC and the selected method covers the actual equipment weight and center-of-gravity. Get the structural confirmation in writing before the permit set is submitted.
Drawing / Submittal Check
For IMC 304.5 (hydrogen-generating and refueling operations): M-001 must identify the hydrogen system type, the quantity and storage location, the ventilation rate for the storage and dispensing areas, the detection and alarming system, and the electrical classification of the hazardous location. Hydrogen system drawings must cross-reference the fire code and the electrical drawings. A hydrogen system permit set submitted without the hazardous location classification and the fire code cross-reference will be returned at routing.
Common Review Risk
Hydrogen system permits require fire marshal coordination in most jurisdictions before the building permit is accepted. A hydrogen system mechanical drawing submitted to the building department without prior fire marshal review will be routed to the fire marshal - adding time. Pre-coordinate with the fire marshal and note the pre-coordination confirmation on M-001. Hydrogen system permits that surprise the fire marshal at the routing stage take significantly longer.
When To Escalate
Escalate for hydrogen system projects where the fire authority and the building authority have different jurisdiction claims - when both agencies believe they have primary authority over the hydrogen storage and dispensing system. Jurisdiction conflicts on hydrogen systems must be resolved at a pre-application meeting attended by all relevant authorities before the permit is filed.
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.
Load Assumption Check
Hydrogen-generating and vehicle-refueling equipment has ventilation loads driven by hazardous gas concentration limits and dilution rates. Confirm the ventilation rate is calculated from the manufacturer's hydrogen output or the applicable dilution formula, not estimated.