Significant changes are on the way for the specification and testing of fire-resistant ductwork. Brian James, technical director of Essex-based Fire Protection, gives HVR his views.
Fire-resistant ductwork has been an essential component of building design since regulations affecting the testing of suitable systems were introduced in 1985.

Following the tragic events at King's Cross station in 1987, when many people were killed or suffered badly through smoke inhalation, building regulations in the UK were changed.

ISO 6944 (1985) was adopted as the test standard for fire-rated ducting - this was renamed British Standard 476 Part 24 (1987) and has since been the main test standard for ducting.

The purpose of this standard is to measure the ability of a ductwork system to resist the spread of fire from one fire compartment to another without the aid of fire dampers.

It should be noted that the test standard relates to a complete ductwork installation - including joints and supports - and concerns its stability, insulation and integrity. The testing standard also differentiates between two types of fire exposure. Type A is where ductwork resists penetration of fire from outside a duct. Type B is where ductwork resists penetration of fire from inside a duct.

Ductwork systems that do not normally contain fire dampers are:

Smoke extract ducts
Pressurisation ducts
Car park extract ducts
Kitchen extract ducts

A general rule, however, is that any ductwork system that is intended to operate, or has a special use, under a fire condition and therefore cannot use fire dampers, will require a fire resistance rating. This means that the ductwork itself must provide the same levels of fire resistance as that offered by the compartment wall or floor, to limit the spread of fire.

Significant changes

The ductwork industry faces significant changes during the next few years, as the current test standards are being replaced by harmonised European standards.

The critical date for change is July 1 2011, when the Construction Products Directive becomes a statutory requirement and BS476 Part 24 (1987) will be withdrawn and the BS EN 12101 series

Product Construction Standards will take precedence. Currently, therefore, specifiers are experiencing a period of coexistence between the two standards and will need to choose between systems devised under the older standards, or those being tested and manufactured to meet the new, higher standards.

It would seem logical that the preference would be to specify products from companies such as Fire Protection that have already embarked on an EN test programme - this may also become the preferred choice of building insurers.

The new BS EN 12101 series Product Construction Standards must be considered alongside the Fire Duct Test Standards plus the Extended Field of Application Standards to achieve the necessary Fire Duct Classification Standards and the resulting CE marking. Each element is critical in ensuring that ductwork meets the required standards of safety when installed.

As tested

The Product Construction Standard ensures that the manufacturer has ISO 9001 quality systems and that the fire-rated ductwork is constructed and installed as tested.

Under the new standard, it will not be permitted to construct fire-rated ductwork from scratch on site - it must be manufactured in the factory and taken to site to be assembled by competent, trained installers.

The Fire Duct Test Standards (BS EN 1366) ensures that the basic product itself is suitably fire resistant. It is a more challenging test than the earlier, superseded BS standard, and still requires ductwork to be tested as built, complete with joints and supports, rather than relying on derived test data based on theoretical calculations. This leads to accurate results under real conditions, resulting in maximum safety in the field.

In order to meet these two requirements, manufacturers will require third-party product certification and independent Quality Assurance certification. When these conditions are met, the manufacturer will be permitted to apply CE marking to such certificated products.

Engineering assessments for fire-resisting ducts larger in cross-sectional area than those tested will no longer be permitted, so specifiers should also be aware that in addition to the above product and test standards, the BS EN 15080 series Extended Field of Application standards have been introduced to deal with all non-standard ductwork and over-size equipment. These standards describe ways in which fire tests may be applied or adapted to suit different arrangements.

Finally the BS EN 13501 series Classification Standards define how the results of the tests should be recorded as a classification showing, among other variables, permitted duct sizes and failure times for ductwork integrity, insulation and reduced leakage.

Fire Protection has already embarked on the stringent testing programme required to meet the new standards. This, combined with its Quality Assurance certification across its two UK factories, will ensure that it is ready to offer a full range of CE-marked products well before the July 2011 implementation date.

Fire Protection believes that anyone currently involved in the design, specification, or installation of any major building project needs fully to understand the implications of the new standards. With the implementation date less than three years away, it is clear that many of these projects will complete during this time.

Under these circumstances, in order to future-proof fire-resistant ductwork installations, the selection of suitable products from a certified manufacturer will become essential, and a company that has already successfully embarked on an EN test programme will be the logical choice.