Overview
ISO 21927-4:2019 specifies design, requirements and installation practices for natural smoke and heat exhaust ventilators (NSHEVs) used in smoke and heat control systems (SHEVS). It covers NSHEVs that extract smoke vertically by thermal buoyancy - via the roof in single-storey buildings and via the uppermost storey in multi-storey buildings - and NSHEVs mounted in external walls. The standard provides tables and calculation methods for designing clear layers, plus guidance on installation, testing, maintenance and integration with other fire protection equipment.
Key topics and technical requirements
- Scope and application: NSHEVs for vertical smoke extraction, plus wall-mounted NSHEVs. Applies to spaces or divided smoke reservoirs.
- Design principles: Key design drivers include rate of energy release, theoretical fire area (design groups), target clear-layer height and space height.
- Clear layer requirements:
- Target clear layer (d) shall be not less than 2.50 m.
- For d ≤ 4 m, smoke barriers must protrude at least 0.5 m into the clear layer.
- For d > 4 m, smoke barrier height shall be at least equal to the smoke layer height (z) and not less than 1.0 m.
- Smoke reservoirs and barriers:
- Maximum smoke reservoir area is 1 600 m²; where needed, spaces shall be subdivided with smoke barriers.
- Maximum distance between barriers (or wall and barrier) shall not exceed 60 m.
- Air inlets:
- Required at low level; area sized based on the largest smoke reservoir.
- Inlets should be located on at least two sides of the building and evenly distributed.
- Doors or windows can serve as inlets if labelled and openable without destructive measures.
- Aerodynamic performance:
- Concepts such as aerodynamic free area and coefficient of discharge (cv) are used to quantify NSHEV efficiency.
- Installation, testing and maintenance:
- The standard includes rules for installation, commissioning, testing, maintenance and repair to ensure reliable operation over service life.
- Integration: Guidance is provided for NSHEVs combined with fire-extinguishing equipment and control systems.
Applications and users
Who uses ISO 21927-4:2019:
- Fire engineers and smoke control designers specifying NSHEVs and SHEVS performance
- Architects and building services engineers integrating smoke vents into building design
- Specifiers, manufacturers and installers of NSHEVs
- Building owners, facility managers and authorities having jurisdiction responsible for fire safety compliance
Practical applications include warehouses, industrial halls, atria and large open-plan spaces where natural buoyant smoke extraction is preferred or required.
Related standards
- ISO 21927-1 - Specification for smoke barriers
- ISO 21927-2 - Specification for natural smoke and heat exhaust ventilators
- ISO 13943 - Fire safety - Vocabulary
For design implementation and compliance, consult the full ISO 21927-4:2019 document and your national standards body.