Passive Fire Protection (PFP) is an integral component of a building’s fire protection; these include passive systems, active systems, means of escape, facilities for the fire service and good building management as defined in both local building regulations as well as national and international standards and codes of practice.

Passive Fire Protection (PFP) is the built-in systems such as walls, floors, doors and fire stopping that resist fire and/or smoke spreading through a building. They generally do not need power or water to operate. Active systems such as sprinklers and alarms do require power or water to operate. In a properly designed building both types of system work together with other fire safety measures to ensure lives and property are protected.

Most modern buildings are designed to provide comfortable indoor environments which are usually provided by an air-conditioning or ventilation ductwork system. Such systems provide a route for fire and smoke to spread rapidly through a building in the event of a fire. The two most common methods used to prevent the spread of fire are to use fire/smoke dampers or fire resisting ductwork.

However, there are certain circumstances under which fire/smoke dampers should not be used. This will normally be confirmed by the fire engineer. In these cases the ductwork itself must provide the same levels of fire resistance as that afforded by the compartment wall or floor. These include smoke extraction, dual ventilation/smoke extraction, car-park extraction, pressurisation and kitchen extract ductwork systems.

When a system is fire resistant it will have been tested to the relevant parts of BS 476 or to a range of EN standards (For example for ducts BS 476: Part 24: 1987 (ISO 6944:1985) or EN 1366-Parts 1, 8, 9) . In these tests the fire protection systems must satisfy various performance criteria which are briefly summarised as follows:

• Stability – The wall, floor or duct must not collapse when exposed to fire.
• Integrity – The fire resistant system must not let excessive smoke or hot gases penetrate into the next fire compartment.
• Insulation – The outer surface of the fire resistant system outside the fire compartment must not get too hot. The maximum permitted temperature must not rise more than 180°C, or as an average of the unexposed surface must not rise more than 140°C. Where a duct is concerned, the approval authority may relax this requirement if the duct is 500mm or more from personnel or combustible materials.
• Kitchen extract – The test standard has a particularly onerous performance requirement which most approval authorities now consider to be unnecessary.
• Smoke extract – The duct must maintain over 75% (For BS/ISO) or 90% (for EN) of its original cross sectional area when exposed to a fully developed fire. The fire engineer/approval authority may only require the duct to extract smoke during the early stages of the fire when the temperatures are much lower. Therefore the duct specification will depend on the requirements of the fire engineer.

As an example, if we consider a duct that must have at least 60min fire resistance, the Firemac FM60 duct system will satisfy most projects but the FM60i system would be needed if fire insulation was requested and the FM60S system would be used when the duct must extract smoke under fully developed fire conditions.

Yes, as discussed in the examples below.

Smoke extraction systems handle the evacuation of products of combustion, which could otherwise pose a life risk. By ensuring breathable air and good visibility, smoke extraction systems aid in evacuation of the building’s occupants and allow fire-fighters to locate the seat of the fire. To extract an adequate volume of smoke and hot gases it is important that as much of the duct’s cross sectional area is maintained. This may mean that the design of the steel ductwork used with the Firemac smoke extract system is more robust than the design used when the Firemac system is used as normal ventilation ductwork.

Dual ventilation/smoke extraction systems serve as a conventional ventilation system under normal conditions but convert to a smoke extraction system in the event of a fire. In this case one must remember to design for the smoke extract function of the duct as discussed above.

Car-park extraction systems which must be both separate and independent, are obligatory in car-parks which require mechanical ventilation to expel polluted air. Due to the fire risk associated with car-parks, these systems should be treated as smoke extract systems and therefore maintain a 75% cross-sectional area under fire conditions in accordance with BS 476: Part 24: 1987 and ISO 6944: 1985 or 90% when using EN 1366-Parts 1, 8 or 9. Generally fire dampers are not to be installed in extract ductwork serving car-parks.

Kitchen extract systems are a major source of fire spread through a building. The grease and oil entering the duct requires that dampers cannot be used and that adequate access panels must be provided for regular cleaning.

Fire Testing and Codes

BS 476: Part 24: 1987 & UL 6944: 1985

BS 476: Part 24: 1987 and ISO 6944: 1985 (used by UL) also requires the duct which is intended for smoke extract to retain more than 75% of its cross-sectional area within the fire compartment. If the ductwork penetrates a fire-resisting barrier, it must be capable of providing the same period of fire resistance as the barrier.

This standard specifies a method of test and performance criteria for the determination of the fire resistance of vertical and horizontal ventilation ducts under standardised fire conditions. The general purpose of the test is to measure the ability of a representative duct or duct assembly to resist the spread of fire from one compartment of a building to another. It does include performance criteria for kitchen extract and smoke extract ducts. The performance of the duct assembly is measured in terms of its ability to withstand exposure to high temperatures by measuring across key performance criteria. Two ducts are tested, one with fire outside only (Duct Type A), i.e. no openings in the room on fire, and one with fire on the inside and outside (Duct Type B), i.e. there are openings in the duct in the room on fire.

Alternative tests are also used in various countries – these include EN 1366-Parts 1, 8, 9 and NFPA 92A as some of the most widely known.

ASTM E2336

ASTM E2336 (UL 2221), Standard Test Methods for Fire Resistive Grease Duct Enclosure Systems only exposes the inside of the duct to fire, and has two stages:

• Stage 1 lasts 240 minutes and represents normal operating conditions at 240° C.
• Stage 2 lasts 30 minutes. The temperature is increased to 1095°C for 30 minutes.

Satisfying the performance criteria for kitchen extract in BS 476: Part 24 (ISO 6944: 1985) requires the duct to be exposed for the full fire resistance period with the fire outside the duct (duct A) and the fire inside the duct (duct B). The ASTM standard E2336 exposes the inside of the duct to similar temperatures for only 30 minutes. The main difference is the requirement to expose the inside of the duct to 240°C for 240 minutes beforehand.

In reality, the duct is unlikely to be run at 240°C outside the kitchen. If ducts are uninsulated, the 240 minute period at 240°C is unlikely to have a noticeable affect.

We are not aware of any recorded examples of fires spreading to other compartments via fire resisting kitchen extract ducts that have been tested to BS 476: Part 24 (ISO 6944: 1985).

NFPA 92: Standard for smoke control systems

This is a guidance document on the containment and management of smoke in buildings. It includes details on design, installation, acceptance testing, operation and on-going periodic testing of smoke control systems. Although this guidance standard refers to specific test standards, it does accept alternative test standards of equivalent level of performance, subject to acceptance by the approval authority for the project. With regards to ductwork, the most relevant document that NFPA 92 refers to is NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilation Systems.

NFPA 90A

NFPA 90A asks that coverings on steel ductwork have low flame spread and smoke development. This can be demonstrated by conducting the Steiner Tunnel Test, however other codes and standards use equivalent tests too, for example, BS and EN tests for smoke, flame and toxic fume.

With regards to fire resistance, NFPA 90A seems to largely rely on dampers. However, it does refer to NFPA 251, Standard methods of tests of fire endurance of building construction and material. This standard has also been withdrawn and the NFPA site states ‘Material found in ASTM E119 and UL 263’. UL 263 does not include a duct test and ASTM E119 is the same as BS 476 series.

Black Steel and Rockwool; The use of insulation materials for fire protection of ductwork in conjunction with Firemac FM Fire Ducts

Firemac FM Fire Ducts that require thermal or acoustic insulation must be insulated with non-combustible insulation material, e.g. a glass or rock mineral wool which is fitted over the Firemac FM Fabric. Class O or combustible acoustic insulation is permitted if fitted inside the duct.

If insulation is required for the purposes of fire protection, Firemac’s construction specification must be followed. The complete duct system, including the design of the steel ductwork, the Firemac FM Fabric and the rock mineral wool, is tested and approved as a complete system. If the fabric is not used this may affect the required specification for the steel ductwork. For example, using the rock mineral wool alone may require thicker steel or more hangers.

If most of the duct run does not need insulation then it makes sense to make the complete run as an uninsulated Firemac system, under controlled workshop conditions, and to apply the insulation on site in the limited areas required. This cuts down on cost and space required.

As a substitute for Firemac FM Fire Ducts

If thermal insulation material is used without the Firemac FM Fabric to provide fire protection, then the insulation manufacturer would have to provide all the supporting test and certification evidence and technical support. If the fabric is used then Firemac provide all of this supporting evidence.

Firemac cannot provide any test evidence to confirm the performance of insulated material in fire conditions, nor any third party certification in support of any claims, unless the Firemac FM Fabric is applied first. If the fabric is not being used, it is important that the contractor consults with the manufacturer of the insulation to review the technical specifications for use as a tested fire duct and ensure that the installation guidelines are followed. Care must be taken that the design of the support system, including the anchors, is sufficient to support the duct and mineral wool in fire conditions. In addition, the designer must ensure that the thermal movement at the wall penetration experienced, when using a fully insulated system, has been anticipated such that the correct fire stopping is used.

If the mineral wool is damaged or removed during the life of the building, the Firemac system will still satisfy the fire stability, integrity (and smoke extraction if required) performance specification keeping the building relatively safe until the mineral wool is replaced. If the Firemac system is not used and the rock wool is damaged or removed then the duct will not satisfy any of these performance criteria.

Black Steel Ducts

Firemac is not aware of any test evidence to confirm the performance of unprotected black steel in fire conditions, or any third party certification in support of any claims. It is not an acceptable form of fire protection for ductwork in the UK and other major European countries because of this lack of test evidence.

Therefore it is important that the contractor consults with the duct supplier to review the technical specifications for the use of unprotected black steel as a tested fire duct and ensure fabrication and installation guidelines are followed. The extra stress the weight of this gauge of steel places on the performance of a duct, its hangers, bearers and anchors in fire conditions, is substantial and contractors and consultants must satisfy themselves that this is a proven method of fire protection, particularly at all penetrations where the greater thermal movement created by the use of such a rigid system will cause the potential for failure and the breaking through of fire into adjoining compartments.

In addition, black steel is an expensive option, when compared to the construction requirements of Firemac FM Fire Ducts which use mild steel, stainless steel or GI depending upon requirements. Ductworkers fabricating Firemac FM Fire Ducts are trained and audited regularly by Firemac, full technical support is given and the performance of Firemac FM Fire Ducts has been tested to 4 hours fire resistance. The system is also listed in the International Fire Consultants Certification (IFCC) scheme and has civil defence approval in the UAE, Oman, Bahrain and Qatar.

Conclusions

• Firemac FM Fire Ducts have been shown by extensive testing to provide up to 4 hours fire resistance.
• The manufacture of the product is supported by third party certification and regular training and inspection by Firemac.
• Insulated Firemac FM Fire Ducts will continue to provide fire resistance, even when the rock mineral wool is damaged.
• Insulated ducts that are not fabricated and installed following the Firemac specification are not supported by the Firemac training and inspection system.
• Firemac are not aware of any supporting test evidence for black steel ducts, which will have much greater thermal movement at wall and floor penetrations and which will apply much greater stresses on supports.

No, the same fabric can be used for all periods up to 240 minutes. The fabric is available in two forms – Firemac FM Fabric PSA, which has a self-adhesive backing, and Firemac FM Fabric WB which is a similar fabric which is secured using Firemac adhesive. Variation in fire performance is obtained by varying the specification of the steel ductwork.

Firemac FM Fire Duct systems are designed to be used as normal ventilation ducts, smoke extract ducts, pressurisation ducts or kitchen extract ducts with fire resistance periods of up to 4 hours when tested to BS 476: Part 24: 1987 (ISO 6944: 1985). Test data is also available to suit the requirements of EN 1366-Parts 1, 8, 9. Their design is based on national codes for steel ductwork such as DW/144 for ventilation ducts and DW/172 for kitchen extract ducts.

This should be detailed in the performance specification for the project. These are often unclear and so the Firemac Technical Manual includes a performance specification questionnaire that the ductworker can send to the specifier to complete. Firemac Technical are always pleased to liaise with the specifier, if requested, to ensure the correct performance will be provided. Once the performance specification is confirmed, the relevant Firemac FM Fire Duct system can be identified in the Selector Chart within the Firemac Technical Manual.

The fire performance specification for smoke extract ducts can be complicated. If the duct penetrates fire compartment walls and floors it will certainly need to have a fire resistance to BS 476: Part 24: 1987 (ISO 6944: 1985). However it may only have to extract smoke and/or satisfy the insulation performance criterion of the standard during the early stages of the fire, i.e. at temperatures of only 300°C or 400°C. On the other hand, the specifier may want the insulation performance or the smoke extract function to be satisfied even during a fully developed fire, i.e. at temperatures around 950°C. The construction specification of the ductwork system will vary depending on the performance required. Firemac’s performance specification questionnaire or Technical Department can help.

In the UK market, if completed duct sections are being sold to a different company to install they may need to be CE marked. If this is the case, contact Firemac for advice before accepting the project.

Firemac FM Fabric is grey in appearance to resemble standard ventilation ductwork, but bears the legend FIRE RESISTANT to ensure other services are not attached to the same hanger support system. However, on occasion, it may be desirable to apply paint to the fabric for cosmetic reasons. This is acceptable as long as the paint used is water based, and customers are encouraged to consult with Firemac prior to application to confirm conformity.

If red oxide paint is used to prevent corrosion in aggressive environments, the Firemac FM Fabric can be bonded to the painted steel using Firemac adhesive without any loss of fire performance.

Firemac FM Blue is, as standard, supplied with a galvanised steel finish. Suitable for use in most environments. However, for areas where there are aggressive industrial concerns e.g chemicals, or salt laden atmosphere e.g coastal regions, Firemac can supply alternative surface finishes, such as stainless steel 316 grade, which are available to order.

Firemac FM Blue can be used for the construction of load-bearing walls and floors, as well as lightweight ceilings and floors that are easily capable of taking foot traffic, maintenance personnel and tools. Please consult your local Firemac office for precise specification of system framing and construction details.

The Firemac FM Fire Stopping products and systems have all been tested in accordance with the requirements of EN standards where relevant as follows:-

Fire-resistant penetration seals, tested in accordance with EN 1366-3.

Fire-resistant linear joint seals, tested in accordance with EN 1366-4.

The Firemac FM Fire Stopping range of fire-resistant seals have been classified up to a minimum of El 120, in accordance with EN 13501-2.

These standards specify a range of pipes (plastic and metallic) as well as cables (single and bundles) and other penetrating items. All the permitted services are detailed in the relevant approval documents.

When completely contained within the fire compartment, ductwork must be capable of resisting the anticipated temperatures generated during the development of a fire. Test Standards include BS 476: Part 24: 1987, EN 1366-Parts 1, 8, 9 and UL 6944.

Firemac FM Fire Ducts are tested to BS 476: Part 24: 1987 (ISO 69441985) and to EN 1366-Parts 1, 8, 9. The Building Research Establishment (BRE) assessment report CC 283899 issue 2 summarises all the fire resistance tests that have been carried out on the Firemac FM Fire Duct systems and describes in detail the range of duct systems that they consider will provide the stated fire performance. Copies of the assessment are available on request.

In addition, Firemac FM Fabric is produced under a third party certification scheme operated by IFC (International Fire Consultants) Certification Ltd.

The duct systems are largely prefabricated in the workshop and installed on site by Firemac trained staff thus improving workmanship. Firemac offer a site inspection service on request.

Thermal / Acoustic insulation

If the insulation is only needed for thermal performance (e.g for air conditioning ducts) and not fire, then non-combustible insulation material should be used, e.g. a glass or rock mineral wool can be fitted over the fabric If acoustic insulation is being applied internally a Class O acoustic foam will normally be acceptable. (There is no requirement for internally fitted insulation to be non-combustible).

Fire Protection

However, if needed for fire protection, Firemac’s specification must be followed for the following reasons:

1. The duct system, including the design of the steel ductwork, the fabric and the mineral wool, is tested and approved as a complete system. If the fabric is not used this would affect the requirements for the steel ductwork. For example, using the rock wool alone may require a thicker steel or more hangers.

2. If the fabric is not used, then the insulation manufacturer would have to provide all the supporting test and certification evidence and technical support. If the fabric is used, then Firemac provide all of this.

3. If most of the duct run does not need insulation then it makes sense to make the complete run as an uninsulated Firemac system, under controlled workshop conditions, and to apply the insulation on site in the limited areas required.

4. If the mineral wool is damaged or removed during the life of the building, the Firemac system will still satisfy the stability, integrity (and smoke extract if required) performance specification keeping the building relatively safe until the mineral wool is replaced. If the Firemac system is not used and the rock wool is damaged or removed, then the duct will not satisfy any of these performance criteria.

Third Party Certification for manufacturers is a system which requires a competent and independent inspection body to carry out audits of the manufacture and supply of fire protection products and that they are being used in the correct applications. Third party certification companies based in the UK are accredited by UKAS.

Firemac FM Fire Ducts are Third Party Certificated by IFCC, a UKAS accredited and internationally recognised provider of third party Certification, with offices in the UK and UAE.