FAQ's & Guides - Flameshield Fireduct - FAQ’s

Q:If I install 1.6mm (16 gauge) steel ductwork constructed to DW 144 where passing through a protected route; is this acceptable as a fire resisting duct?

A:No, ductwork passing through a protected corridor should be fire resisting when tested to BS 476: Part 24 or EN 1366-1 (with fire exposure from the inside) and not serve the protected route for the required period of fire time. An alternative to using a fire resisting duct would be to use ES classified leakage rated fire dampers. Such dampers should achieve an ES classification to BS EN 13501-3 when tested to BS EN 1366-2.

Q:Can general purpose DW 144 ventilation / air conditioning ductwork be utilised as, or converted into a fire resisting ductwork system?

A:No, a converted or modified ductwork cannot be utilised as a fire resisting ductwork system unless the construction / materials of the whole system are proven by tests in accordance with the requirements of BS 476 Part 24 (refer ASFP Blue Book “CAUTIONARY NOTE TO ALL DUCTWORK DESIGNERS, MANUFACTURERS AND INSTALLERS”).

Q:Does ductwork necessarily require external spray to achieve fire resistance?

A:No, the only requirement is that the system is proven by test, either BS 476 Part 24 or BS EN 1366 Parts 1, 8 & 9.

Q:Does ductwork passing through a protected route need additional fire rating if it has been fitted with fire dampers when entering and leaving a corridor or stair enclosure?

A:Yes, fire dampers are not designed to protect against smoke which is a concern for protected escape routes. A closed fire damper will still leak a considerable quantity of smoke. Fire dampers will NOT prevent heat conduction and radiation from distorting the ductwork in the escape route which might lead to cause joints to open up and contaminate the escape route. Therefore the ductwork would need an additional fire resisting enclosure tested to BS 476 Part 24 or EN 1366-1 (with fire exposure from the inside) and not serve the protected route. However, if you would prefer to use dampers and not protect the duct this is possible but the dampers would need to ES classified leakage rated dampers and must achieve an ES classification to BS EN 13501-3 when tested to BS EN 1366-2. These dampers are considered to have good smoke resisting properties in addition to fire resistance.

Q:Would metal ductwork wrapped in mineral wool be acceptable to protect ductwork passing through a protected route as a means to protect the ductwork?

A:No, unless proven by test, either BS 476 Part 24 or BS EN 1366 Parts 1, 8 & 9.

Q:Would a duct having Class O fire rating be acceptable in a protected route as a means to protect the ductwork?

A:No, class O does not refer to fire resistance.

Q:Is it a mandatory requirement to insulate fire resistant kitchen extract ductwork outside the kitchen area?

A:No, however serious consideration should be given for the following reasons;

1. If the duct is un-insulated, such a system will not ensure that the temperatures on the inner surface of the ductwork will not exceed the temperature limits of the standard when the duct is attacked from outside the duct. In practice this could mean that if there was a fire in the room next to the kitchen for example, this could cause the ignition of grease and fat that has built up within the duct, and this could lead to a fire spreading back to the kitchen.
2. If the duct is un-insulated, such a system will not ensure that other services, in close proximity, are protected from the effects of radiated heat through the external surface of the duct.
3. If the duct is un-insulated, and is located over an area offering a means of escape, such a system will not ensure that there is adequate protection to negate the effects of radiated heat which might cause some personal injury to persons evacuating the building.

Q:Am I able to support fire resisting ductwork from timber constructions?

A:Yes, however there are guidelines which MUST be rigidly adhered to. As a basic guide the fire resistance of the supporting structure must always be at least equal to the fire resistance of the ductwork system. Likewise the fire resistance of the ductwork must always be at least equal to the fire resistance of the building compartmentation through which the ductwork is passing.

Q:Is it mandatory that all companies manufacturing and installing fire resisting ductwork are required to be third party certified?

A:No, however most end users and building insurers recognise the benefits of being certified and being part of a third party auditing scheme.

Q:Are all installers required to be formally trained to install fire resisting ductwork?

A:No, however companies who are certified by one of the accredited installer schemes are required to illustrate that ALL operatives have received the correct training and are regularly subject to both internal and external appraisal. There are two such accredited schemes currently in operation, those being the FIRAS scheme, which is administered by Exova Warringtonfire, and the LPCB LPS 1531 Installer Scheme which is administered by BRE LPCB (Building Research Establishment Loss Prevention Certification Board).

Q:Which of the two-installer schemes are best?

A:Both schemes offer the same level of certification and are both accredited and subject to third party auditing from UKAS (United Kingdom Accreditation Service).

Q:Do either the FIRAS or LPS 1531 schemes cover both the manufacturing processes and the installation of the product?

A:No, both schemes solely cover the installation element of the works. All other processes come within the remit of the company quality plan i.e. ISO 9001:2008.

Q:Should I be insisting, when choosing a fire resisting duct product, that it is tested to the new BS EN 1366 Part 1 & 8 test standards?

A:We recommend choosing BS EN 1366 tested fire resisting duct product. The EN 1366 standard goes beyond BS 476 with more test scenarios and criteria to meet making it a safer and superior product.

Both test standards (BS 476 Part 24 and EN 1366 Parts 1, & 8) are currently accepted. Building Regulations Approved Document B does not preclude the use of ventilation or smoke extract ducts being constructed and installed in accordance with the test standards BS 476 Part 24, it is entirely within the control of the relevant local authority building control officers to make a decision. The new European test standards are therefore not currently a mandatory requirement and cannot be uniquely specified. However, in anticipation of the new standards becoming mandatory at some time in the future some level of comfort might be taken from companies who have completed a test programme in compliance with these standards and are able to illustrate that they have published ALL of their classification documents and made a “Declaration of Performance” which is issued into the public domain.

Q:What can I expect from a company with third party certification when the project installation is complete?

A:Fully traceable inspection/sign off sheets and the issue of a “Certificate of Conformity” confirming that the manufacture and installation has been completed in full compliance with the standards of the tested product.

Q:What action is needed where fire-resisting ducts pass through oversized openings in fire resisting elements of construction?

A:Any oversized gap shall be reduced in size such that the additional fire penetration seal around the duct can function as fire tested within a maximum residual opening.

Responsibility for the satisfactory performance of each element of the building construction (e.g. walls, floors, cavity barriers, etc.) lies with the installer of each particular element. The ‘change over’ of responsibility occurs at the interface between the fire resisting ductwork and the elements. It is imperative that the interface detail does not compromise the fire performance of either the element of building construction or the fire rated duct. The building designer, mechanical services designer and the installer all have a responsibility to pay ‘due care’ to this detail.

Q:What actions should be taken when improper fire resisting duct mounting is evident?

A:Ordinarily, contact the installation contractor and confirm that there has been relevant fire testing and competent assessment on the system. If there is no satisfaction then contact the main contractor/employer/CDM Coordinator to raise any concerns. Ultimately contact the local enforcing authority.

Q:Can test results for rectangular ductwork be used for circular or flat oval ducts: circular or flat oval ‘spiral wound’ ducts: and flexible ducting systems’?

A:The answers are different for those ducts tested to BS 476 Part 24 or tested to BS EN 1366 test methods.

In the case of BS 476 Part 24 test data, circular and flat oval straight seamed and spirally wound steel ducts may be assessed on the basis of the test on rectangular ducts. Details of the construction of circular and flat oval, straight seamed and spirally wound steel ducts must be provided by the duct manufacturer. Further details are provided in ASFP ‘Blue Book’ publication ‘Fire resisting ductwork’ – 2nd Edition Section 6.2.1.10’

In the case of the BS EN 1366 test data, no equivalence is permitted and all ductwork systems much be individually tested. The published European DIAP and EXAP rules apply.

As the vast majority of fire test on ducts are conducted with rigid ducts it is not appropriate to extrapolate this data for flexible ducts. Therefore, unless the flexible duct system has been fire tested, the guidance cannot be assumed to apply.

Q:What is meant by ‘field of application’ of test results for fire resisting ductwork?

A:The answer comes in two parts. DIAP and EXAP rules are an output from European harmonization of fire testing methods and classifications. At a national level, experienced persons or fire test organisations have previously provided assessments of expected performance based on expert judgment.

1. The direct field of application (DIAP)
   DIAP rules are provided in BS EN 1366 test standards. They are derived form information obtained from tests carried out in accordance with relevant EN 1366 tests at recognized laboratories in Europe. The test results achieved by a particular design may be directly applied to a limited number of variations (e.g. a reduction in duct size) without recourse to expert advice, providing the design remains substantially as tested.
   
   The scope of the current BS 476 test method does not consider the effect, detrimental or not, that variations in the test construction may have on the achieved performance of the duct. The test result only applies to the tested design and size; the field of direct application is very limited. The ASFP ‘ Blue Book’ publication ‘Fire Resisting ductwork – 2nd Edition’ contains information in Section 6.
2. The extended field of application (EXAP) rules are derived from test evidence to relevant BS EN 1366 test standards and is provided in the relevant section of BS EN 15080. EXAPs shall be based on primary test evidence to BS EN 1366 and may be supplemented by appropriate test evidence generated from other sources, or other relevant historical data.
   
   The EXAP rules consider changes in the tested design beyond the scope of direct application and may also consider variations to the tested design. For example, an increase in duct size which necessitates the inclusion of a joint in the duct walls.