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Chapter 4 — SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY AND USE

421 Hydrogen Fuel Gas Rooms — 2025 California Building Code

California Building Code (Title 24, Part 2) · 2025 edition · updated 2026-09-25 · California

CBSC: official editions, supplements and errata

Italicized text is a California amendment to the model code, as printed in the official publication.

Cite as: 2025 California Building Code (Title 24, Part 2) § 421 · Effective January 1, 2026 · Official source: Building Standards Commission

[F] 421.1 General. Where required by the California Fire Code, hydrogen fuel gas rooms shall be designed and constructed in accordance with Sections 421.1 through 421.7.

[F] 421.2 Location. Hydrogen fuel gas rooms shall not be located below grade.

[F] 421.3 Design and construction. Hydrogen fuel gas rooms not classified as Group H shall be separated from other areas of the building in accordance with Section 509.1.

[F] 421.3.1 Pressure control. Hydrogen fuel gas rooms shall be provided with a ventilation system designed to maintain the room at a negative pressure in relation to surrounding rooms and spaces.

[F] 421.3.2 Windows. Operable windows in interior walls shall not be permitted. Fixed windows shall be permitted where in accordance with Section 716.

[F] 421.4 Exhaust ventilation. Hydrogen fuel gas rooms shall be provided with mechanical exhaust ventilation in accordance with the applicable provisions of the California Mechanical Code .

[F] 421.5 Gas detection system. Hydrogen fuel gas rooms shall be provided with a gas detection system that complies with Sections 421.5.1, 421.5.2, and 916.

[F] 421.5.1 System activation. Activation of a gas detection alarm shall result in both of the following:

  1. Initiation of distinct audible and visible alarm signals both inside and outside of the hydrogen fuel gas room.
  2. Automatic activation of the mechanical exhaust ventilation system.

[F] 421.5.2 Failure of the gas detection system. Failure of the gas detection system shall automatically activate the mechanical exhaust ventilation system, stop hydrogen generation, and cause a trouble signal to sound at an approved location.

[F] 421.6 Explosion control. Explosion control shall be provided where required by Section 414.5.1.

[F] 421.7 Standby power. Mechanical ventilation and gas detection systems shall be provided with a standby power system in accordance with Section 2702.

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▸Contents — California Building Code (Title 24, Part 2)
California Building Code (Title 24, Part 2)

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