The basic principle behind passive fire protection is compartmentation. This compartmentation is mainly achieved through fire separations. However, since most deaths are actually caused by smoke and not fire, smoke separations are also part of compartmentation and perform a vital role in protecting life.
Some short definitions can be found in documentation such as the Acceptable Solutions:
Smokecell: A space within a building that is enclosed by an envelope of smoke separations or external walls, roofs, and floors
Smoke lobby: That portion of an escape route within a firecell that precedes a safe path or an escape route through an adjoining building that is protected from the effects of smoke by smoke separations.
Smoke separation: Any building element able to prevent the passage of smoke between two spaces. Smoke separations shall:
a) Be a smoke barrier complying with BS EN 12101 Part 1, or
b) Consist of rigid building elements capable of resisting without collapse:
i) a pressure of 0.1 kPa applied from either side, and
ii) self-weight plus the intended vertically applied live loads, and
c) Form an imperforate barrier to the spread of smoke, and
d) Be of non-combustible construction, or achieve an FRR of 10/10/-, except that non-fire resisting glazing may be used if it is toughened or laminated safety glass.
COMMENTS: The pressure requirement is to ensure rigidity and is not a smoke leakage requirement.
Walls and floors, whether constructed of sheet linings fixed to studs or joists or of concrete, glazing, metal or fired clay, need only be inspected by someone experienced in building construction to judge whether the construction is tight enough to inhibit the passage of smoke.
Item d) is intended to ensure that the smoke separation will continue to be an effective barrier when exposed to fire or smoke for a short period during fire development. There is no requirement for smoke control doors or other closures in smoke separations to meet the provisions of item d)
Smoke Stop: A material or construction method used to restrict the spread of smoke within or through fire separations or smoke separations. Smoke stops are mainly used to seal around penetrations but can also be used to seal narrow gaps between building elements.
We can conclude that smoke separations are the method for preventing the spread of smoke into adjoining areas by introducing smoke-resisting elements (e.g. walls, floors, doors, ducts). Besides being enforced by law, by following these requirements, lives are being saved.
A smoke separation may be assumed to be imperforate if, by visual inspection, there are no holes, gaps or openings that would permit smoke passage.
The applicable New Zealand Building Code (NZBC) requirements to smoke stopping are to safeguard people from an unacceptable risk of injury or illness caused by fire. Specifically, Clause C3.1 states that buildings must be designed and constructed to have a low probability of injury or illness to persons not close to a fire source. The compliance requirements may come from different sources, as below.
The NZBC definition of smoke separation refers BS EN 12101 Part 1 as a means of compliance. This standard defines both allowable gaps around the smoke separation edges, and the smoke separation's permitted permeability. Depending on the smoke separation shape, BS EN 12101 Part 1, compliance can allow leakage areas equating to a few percent of the smoke separation.
Acceptable Solutions (e.g. C/AS2) state that gaps shall be sealed with fire-resistant materials complying with AS 1530.4 to avoid smoke passage through fire and smoke separations.
C/AS2 Amendment 2 (5 November 2020) – Acceptable Solution for Buildings other than Risk Group SH. (Table 4.2) contains the following values for Insulation and smoke stop capability of closures in fire and smoke separations Paragraph 4.16:
When different fire-resistant ratings (FRRs) apply on each side of fire separation, being a wall, the higher rating shall apply to both sides.
AS1530.4 stipulates a 200°C maximum temperature provision for smoke barriers and does not provide any controls on smoke leakage except for fire and smoke dampers, where section 11.6 permits a maximum smoke damper leakage rate of 200m³/(h/m²), at 300Pa during the first five minutes of the fire test (corrected to standard temperature and pressure). This increases to 360m³/(h/m²) for fire dampers. It also states that significant smoke spread or smoke production can occur even though an element of construction may have achieved a high fire resistance level (FRL). Other test methods, such as AS 1530.7, may be considered when evaluating the potential for smoke spread.
BRANZ Study Report No148 (2006), which examined the tenability in exit ways, suggested a maximum measured air leakage rate through doors, at ambient or medium temperature conditions, 25 and 40 m³/hr single and two leaf doorsets, respectively.
FPANZ Position Statement PFPS-04 Fire and Smoke Stopping Methodology - provides background to the NZBC expectations to minimise smoke leakage/spread. It is intended to highlight how the design and details of smoke stopping construction could be defined.
Notes: All fire and smoke walls are required to have smoke control doors and walls surrounding a smoke control door must be a smoke separation.
From C/AS2:
· Doorsets installed in fire separations between firecells and vertical safe paths or protected shafts shall have smoke seals on all edges.
· Doorsets shall be clearly marked to show their FRR and, if required, to show their smoke stopping capability. Smoke control doors shall meet the requirements for smoke separations.
· Smoke control doors shall be provided at smoke separations in vertical safe paths, and where a corridor or an escape route passes through a smoke separation, and between an open path and a smoke lobby.
Product manufacturers should be contacted to confirm if their product or assembly meets a smoke separation requirement in other respects.
Check also our article in Fire Separations.
Nelligan Consulting Engineers has the expertise to help with the specification and detailing of smoke separations on your Fire Safety Design, including Fire Engineering solutions and Passive Fire Protection systems.