Overview
ISO 21805:2023 provides guidance and recommendations on the design, selection and installation of vents to protect the structural integrity of enclosures that are fitted with fixed gaseous fire‑extinguishing systems. The standard addresses both over‑ and under‑pressurization venting during agent discharge and post‑discharge venting (extract) to meet requirements in ISO 6183:2022 and ISO 14520‑1:2023. It is intended as supplementary guidance (not a replacement for manufacturer instructions) for pressure management and gas retention in total‑flooding gaseous systems.
Key topics and technical requirements
- Pressure‑relief venting principles - managing positive and negative pressure excursions during discharge to avoid structural damage while preserving agent retention (hold time).
- Vent area calculations - methods based on test-derived correlations between leakage‑to‑volume ratio (LVR) and peak enclosure pressure (PMAX). Separate approaches and agent‑specific considerations for non‑liquefiable, liquefiable gases and CO2.
- Agent effects and humidity - humidity corrections for halocarbon agents (FK‑5‑1‑12, HFC‑23, HFC‑125, HFC‑227ea) based on test data; LVR vs PMAX correlations derived at nominal test conditions (21 °C, ~38 % RH).
- Vent types and characteristics - gravity, counterweighted, electrically or pneumatically operated vents, vent accessories, vent efficiency, minimum opening/closing pressures and fire ratings.
- Vent location and mounting - recommendations for placing vents, mounting details and consideration of leakage (equivalent leakage area, ELA) normalized to an effective pressure (125 Pa) with a reference discharge coefficient (0.61).
- Advanced calculations and arrangements - cascade venting, venting into adjacent enclosures, and guidance for deriving agent‑specific formulae (Annex A and Annex B).
- Safety, acceptance and maintenance - structural and personnel safety considerations, acceptance testing, and service/maintenance guidance (note: does not provide full installation/service specifications).
Applications and users
ISO 21805:2023 is practical for:
- Fire protection designers and system engineers specifying venting for gaseous total‑flood systems
- Building services and mechanical engineers responsible for enclosure integrity
- Installers, commissioning agents and maintenance teams performing acceptance and servicing
- Facility managers and authorities having jurisdiction verifying compliance with ISO 6183 and ISO 14520 series
- Manufacturers developing agent‑specific venting guidance and test procedures
Related standards
- ISO 6183:2022 - requirements referenced for vent area calculations (CO2 cross‑reference)
- ISO 14520‑1:2023 - gaseous extinguishing system requirements (venting and post‑discharge)
- Annex A/B of ISO 21805 - methods for deriving agent‑specific coefficients and test guidance
Keywords: ISO 21805:2023, pressure‑relief vents, gaseous fire‑extinguishing systems, vent area calculations, LVR, PMAX, post‑discharge venting.
Open preview (PDF)Guidance and recommendations on design, selection and installation of vents to safeguard the structural integrity of enclosures protected by gaseous fire-extinguishing systems
