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A new international standard allows specifiers much greater choice

The International Standards Organisation produces standards that can be adopted by any country around the world where the subject of the standard is not already covered by an existing National or Continental standard.

Traditionally UK manufacturers of mechanical and intumescent fire dampers have tested in accordance with BS476 Part 20 but the pressure regime and leakage criteria in this test are not appropriate to the conditions encountered during a fire in ventilation systems. More recently, leading manufacturers of mechanical dampers have tested in accordance with the European fire test standard EN 1366-2:1999 ‘Fire resistance tests for service installations - Part 2: Fire dampers’ which requires pressure differentials and leakage criteria more appropriate to the conditions experienced when ducted ventilation systems are exposed to fire.

EN 1366-2 was adopted almost unchanged as an ISO standard and published as ISO 10294-1. This has been used by manufacturers selling dampers to markets outside of Europe. Unfortunately the pre-fire test requirements in EN1366-2, having been specifically written for mechanical fire dampers, can not be applied to intumescent dampers. Consequently manufacturers had no wholly relevant fire test standard to demonstrate the performance of intumescent dampers.

It is therefore not surprising that many specifiers were reluctant to incorporate intumescent dampers in their projects’ specifications without the comfort of appropriate test evidence.

However, in April 2005 the International Standards Organisation published a new standard ‘Fire resistance tests – Fire dampers for air distribution systems – Part 5: Intumescent fire dampers’ which has been published in the United Kingdom as BS ISO 10294-5. The standard defines the operating conditions during a fire test and the relevant pass/fail criteria, but also provides guidance on how durability and reliability can be demonstrated to establish a product’s fitness for use.

At last intumescent dampers can be tested in conditions appropriate to their intended use, and ventilation system designers can benefit from the versatility of design solutions and cost savings that good intumescent dampers can provide.

To comprehend the importance of this new development it is necessary to review the historic background of mechanical and intumescent dampers.


One reason that EN1366-2 is not considered an appropriate test method for intumescent dampers is the interpretation often made of the definition of ‘fire damper’ it contains. “A mobile closure within a duct which is designed to prevent the passage of fire”. This has been interpreted as meaning that a damper must have mechanically moving plates that slide, drop or rotate into the closed position. The English dictionary however gives a different definition of mobile - “easily moved; changing; vacillating; mechanised; capable of moving rapidly from one place to another”. Obviously a misleading definition and misguided interpretations have given rise to the argument that EN1366-2 is not intended as a test method for intumescent dampers.

For the sake of clarity in this article, the following definitions will be used:

  • Mechanical fire damper: a damper that employs mechanically driven moving parts, and is activated by a thermal release mechanism or fusible link.
  • Mechanical fire and cold smoke damper: a mechanical fire damper which incorporates an electrically driven device that interfaces with smoke sensors.
  • Intumescent fire damper: a damper which closes when activated by heat.
  • Intumescent fire and cold smoke damper: an intumescent fire damper which incorporates electrically driven plates and is interfaced with smoke sensors.

Intumescent fire and cold smoke dampers can be tested in accordance with EN 1366-2 since such products can comply with all the requirements of pre-testing and conforms to the existing definitions.

Technology - State Of The Art

Many people are not yet conversant with modern intumescent damper designs and therefore dismiss them as inadequate for the purpose based on their knowledge of yesteryear. Modern intumescent dampers, such as those manufactured by Lorient Polyproducts Ltd., will maintain their fire stopping performance in extremely hostile conditions of moisture and airborne contaminants. With excellent aerodynamic characteristics and low pressure differential values in normal use, they resist clogging and therefore require little or no maintenance.

They are not affected by failure due to distortion caused by poor installation and will always seal when exposed to heat regardless of the level of build up of debris and other contaminants. Whilst resisting pressure differentials well in excess of the prescribed 300Pa under fire conditions, their leakage performance is greatly superior to most mechanical damper equivalents. Additionally, Lorient fire dampers provide a period of insulation which is not the case for standard mechanical fire dampers

In 2004 the Building Research Establishment (BRE) conducted fire integrity tests of mechanical dampers side by side with an intumescent damper on behalf of the Office of the Deputy Prime Minister (ODPM). as part of an investigation into the efficacy of fire dampers

During the test where all the dampers installed in sections of duct were exposed to the same furnace simultaneously, the intumescent damper closed before either of the mechanical dampers despite the thermal release mechanisms on the mechanical dampers being set to activate at 74°C. Thus was dismissed the argument that intumescent dampers are too slow to react in fire conditions.

After closing, the temperature downstream of the unexposed face of the intumescent damper did not exceed 100°C. for the duration of the test. The downstream temperature of a small single blade mechanical damper rose to over
330°C. after 40 minutes, and the downstream temperature of a large multi-blade mechanical damper rose to over 500°C. during the test. Thus the superior insulation quality of the intumescent damper was clearly demonstrated, together with its ability to prevent secondary ignition of combustible deposits in the downstream duct.

What next?

The advent of BS ISO 10294-5 will now allow manufacturers to provide unequivocal test evidence of intumescent fire damper efficacy in ducts and will give specifiers the confidence to select these products as cost effective alternatives to conventional mechanical fire dampers. They will be able to take advantage of the simplified installation requirements; more compact slim-line product dimensions; minimal maintenance and height and width dimensions to suit almost any duct configuration.

Future Fire Standard Activities.

The current European fire test standard EN 1366-2:1999 is in the process of revision and the UK Government is supportive of the argument that the revision should incorporate Intumescent Fire Damper requirements. In parallel with this revision, a new fire damper product standard is being drafted that is intended to incorporate the requirements of both mechanical and intumescent dampers. A classification standard prEN 13501-3 that is in the late stages of draft will also have to be revised to accommodate intumescent dampers.

A European ‘Technical Report’ is in an advanced state of drafting which, when published, will give guidance to Authorised Bodies, Test Laboratories and Manufacturers on the means by which intumescent products shall be demonstrated to satisfy ‘fitness for use’. The Technical Report will apply not only to components of intumescent dampers but also to mechanical dampers that incorporate performance enhancing intumescent materials in their construction.

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Article written by Phillip Horton, Fire Engineering Solutions.