DS 428 — Ventilation and fire

DS 428 is the Danish standard that sets out the fire-technical requirements for ventilation systems in buildings. Its full title is "Standard for fire protection measures for ventilation systems". The current edition is DS 428:2019 — the fourth generation — which superseded DS 428:2011 and DS 428-3:2009. The AMU compendium Teknisk brandisolering — Ventilationskanaler (Preben Kristensen, the Danish Ministry of Education 2011), the foundation of this article, describes the transition from the old DS 428 and the phasing-in of the European fire classes [AMU compendium pp. 4-5].

Where DS 452 covers thermal insulation (energy, heat loss), DS 428 is its parallel in the fire domain. The two standards often apply simultaneously to the same duct.

DS 428 is a legal requirement. If you install ventilation fire insulation incorrectly, or use a product that is not certified to the standard, the installation is in legal terms unlawful — and you bear a personal legal responsibility both for carrying out the work lawfully and for reporting unlawful installations by others [AMU compendium p. 4].

Who decides legality? In practice, the technical administration in the municipality together with the fire inspector. The independent DBI (the Danish Institute of Fire and Security Technology) is an Approved Technological Service company with great influence — DBI tests products and advises on regulations. If you disregard the guidance of DBI and Dansk Standard, the installation is in principle unlawful [AMU compendium p. 5].

As a GF2 student you must be able to read the project documentation, understand the fire-technical designations, and carry out the installation exactly as the tested system prescribes. A deviation of a few millimetres or a switch of product along the way can cost the fire approval.

DS 428 covers: All new ventilation systems in non-small buildings — multi-storey housing, offices, shops, schools, hospitals, care homes, industry, warehouses, restaurants. Both mechanical and natural ventilation [AMU p. 4]. The standard covers duct systems, fire dampers, penetrations, the installation of units and fans, as well as smoke ventilation (in conjunction with DBI guideline 27).

DS 428 does NOT cover:

• Smoke ventilation as a primary fire strategy — that lies in DBI guideline 27 / DS/EN 12101
• Thermal insulation — that is DS 452 (often applies simultaneously)
• Building structures — that is BR18
• Single-family houses with simple extraction (kitchen hood, toilet extraction) — may be exempted [AMU p. 24]
• Cooling systems with explosive charges — require a separate assessment [AMU p. 22]
• Process-industry ventilation (ATEX, explosion) — has its own rules

For air volumes, energy and dimensioning, DS 447 — Standard for mechanical ventilation systems applies.

BR18 divides buildings into fire compartments (typically EI 60-120 — large units such as an entire dwelling or floor) and fire cells (typically EI 30-60 — smaller units such as single rooms). These separations give the escape routes time: when a fire breaks out, the walls, floors, ceilings, doors and penetrations must keep the fire contained long enough for everyone to get out.

The problem with ventilation: A duct is a large hole that breaches many compartments and cells. Without treatment, fire and hot smoke can be pumped at up to 10 m/s from the basement to all floors, from one dwelling to its neighbour.

DS 428's main principle:

The ventilation system must not degrade the building's division into fire compartments and fire cells.

Where the duct crosses a fire separation, fire-technical measures must be taken so that the crossing is at least as fire-resistant as the wall it passes through. If the duct crosses an EI 60 wall, the penetration and the continuation of the duct must also be EI 60. It is this simple logic that drives all the detailed rules in DS 428.

DS 428 gives the insulator and the consultant four basic tools to solve the problem. Each tool has its area of use, and typically several of them are combined in the same installation:

1. Fire insulation of ducts — the duct is "wrapped" in a tested, certified fire insulation, so that the entire duct in itself achieves a particular EI class (EI 30, EI 60, EI 90 or EI 120). Used when a long duct run passes through several fire compartments, or when the duct hangs externally along an escape route and must protect it. The class is selected by the design engineer on the basis of the building's use category and fire strategy.

2. Fire dampers (automatic dampers) — a damper is mounted in the penetration itself; under normal operation it stands open, but it automatically closes in a fire. The damper can be triggered thermally (melts at approx. 70 °C), electrically (a signal from the central system) or differentially (a smoke sensor). When the damper is closed, it acts as a fire-compartment separation in itself. Used when the duct is not fire-insulated but crosses a compartment — typically in installation shafts and at connections to room diffusers [AMU compendium pp. 11-13].

3. Fire sealing at penetrations — the hole itself in the wall or floor slab, where the duct passes, is sealed with a tested fire-sealing product: stone wool batts combined with fire sealant, fire mortar, a fire collar or special fire-retardant water-glass adhesive. Ensures that no fire or smoke can escape through the gap between the duct and the wall [AMU compendium pp. 25-27].

4. Smoke ventilation and controlled smoke extraction — instead of closing everything off, the smoke can be controlled by actively extracting it via dedicated smoke-extraction ducts. This is called a smoke-ventilated system. It is a completely different strategy from the other three tools, and typically requires special fans, smoke-evacuation dampers (RES) and fire-rated ducts. Smoke ventilation reduces the need for fire dampers but increases the requirement for the duct's fire insulation [AMU compendium p. 14].

In practice, tool 1 (fire insulation) + tool 3 (fire sealing) are typically combined on most duct runs, supplemented by tool 2 (fire damper) where relevant. Tool 4 (smoke ventilation) is a project decision made early on by the fire consultant.

The fire class consists of letters (criteria) + numbers (minutes). The classification standard is EN 13501-3 for ducts and dampers. The most important criteria:

• R — Load-bearing capacity (load-bearing structures only)
• E — Integrity. The duct remains tight — no flames or hot gases pass through [AMU compendium pp. 5-6]
• I — Insulation. The surface on the unexposed side may rise no more than 140 °C on average, 180 °C at a single point [AMU compendium p. 9]
• S — Smoke tightness (Smoke) at ambient temperature — a requirement for dampers [AMU p. 6, 12]
• More rarely: W (radiation), M (mechanical), C (self-closing), G (chimney fire), K (fire-protection capability)

The numerical value indicates minutes: 15, 30, 60, 90 or 120. In practice 30-120 min are used [AMU p. 7].

Use category is added in parentheses: ho (horizontal), ve (vertical), i↔o (fire from inside AND outside — required in Denmark) [AMU p. 7].

DS 428 has used EN 1366-1 as the test method since 2009 (replacing NT Fire 034). Denmark requires a "duct B" test, i.e. fire both inside and outside — this is "i↔o" in the classification.

The Danish standard class is:

EI 30/E 60 (ve ho i↔o) A2-s1,d0

That is: 30 min for both E and I, then 30 min more of E only. A2-s1,d0 = non-combustible with limited smoke, no flaming droplets.

The material class (EN 13501-1) is written after the EI class:

• A1 = fully non-combustible (stone wool/glass wool without binder)
• A2-s1,d0 = non-combustible, low smoke, no droplets (standard for finished mineral-wool fire products)
• B-s1,d0 = very limited fire contribution (fire-retardant foams)
• E = ignitable (ordinary PUR)
• F = not tested

For fire insulation, A2-s1,d0 or A1 is almost always required [AMU pp. 7-8].