FIRE DAMPERS - A CASE OF 'BETTER SAFE THAN SORRY'?
25/03/2010
Fire damper under test
Fire damper under test
Barry Trewhitt, TROX Product Manager – Systems, reviews the legislation on fire dampers and questions whether just meeting the minimum requirement is a risky strategy.
The regulations on fire dampers are in a period of transition, and that’s not particularly helpful for building services engineers. Two sets of testing standards are currently running side by side and, as they are very different from one another, anyone specifying these products has to understand the full implications of each to make an informed decision.
Tens of thousands of fire dampers are specified and installed in the UK every year. Under the requirements of the Building Regulations Approved Document B Part 20, openings in a cavity barrier are limited to:
Doors which have at least 30 minutes fire resistance.
Passage of pipes meeting Part B requirements
Passage of cables and conduits
Openings fitted with a suitably mounted automatic fire damper.
Ducts which (unless they are fire-resisting) are fitted with a suitably mounted automatic fire damper where they pass through the cavity barrier
The traditional standard in the UK for testing of products such as fire dampers has, for many years, been BS 476-20:1987 Fire tests on building materials and structures – Part 20: Method for determination of the fire resistance of elements of construction (general principles). It has been widely accepted however that BS 476-20 has its limitations, and that a testing standard was needed, which dealt specifically with fire dampers.
At the same time there has been an intention, across the EC Member States, to harmonise national standards into single Europe-wide standards to assist trade between countries. The result has been the creation of a dedicated testing standard for fire dampers – the European Standard BS EN1366-2 – which is expected to replace, at some stage in the future, the various national testing standards across Europe.
As you can imagine, getting every Member State to agree has presented a challenge. So, until the British standard is withdrawn, a manufacturer who wishes to place a fire damper product on the UK market can now test and classify products by either the national UK standard or the European one.
Choosing between products tested to BS or EN standards wouldn’t normally be a life or death decision for a specifier. But fire dampers are different. By the nature of the role they perform, they have the potential to be the weak link in a wall/fire break. Bearing in mind the safety-critical nature of the product, it is essential that specifiers have a clear understanding of what the various product ratings actually mean.
Setting the standard
We are accustomed to the UK demanding more stringent standards than our European counterparts. The opposite applies in the case of fire dampers however. The bar is set lower for UK products, whilst products sold into Germany, France and so on, have to pass additional and more stringent tests before they are allowed on the market.
This means that there are many applications in which a BS standard product, whilst meeting the minimum requirements of the Building Regs, may not be the best option.
Where to opt for EN 1366-2 classified fire dampers
There are some circumstances in which Part B already demands the use of European Standard fire dampers. This includes:
5.48 Fire dampers activated only by fusible links are not suitable for protecting escape routes. However an ES classified fire and smoke damper which is activated by a suitable fire detection system may be used.
10.13 Where the use of the building involves a sleeping risk, such as an hotel or residential care home, fire dampers should be actuated by smoke detector-controlled automatic release mechanisms, in addition to being actuated by thermally-actuated devices.
Having studied the performance of both BS 476 and EN1366-2 products during fire testing however, TROX believes that many UK projects (particularly those where evacuation of occupants could pose challenges) are missing out on the necessary levels of fire protection during this period of transition. This may be due, in part, to a misconception that the two testing regimes are equally stringent. This is not the case.
Differences
Each of the standards has been designed to test how good a fire damper is at ‘buying time’, allowing occupants to evacuate, and the fire service to take control. The testing methodologies of the two standards differ significantly however. The performance criteria for the BS 476 standard requires that the fire damper is able to :-
The European discussions however focused on the fact that smoke poses an equally dangerous threat. The BS 476 standard does not demand the measurement of the leakage of hot gases through the fire damper. Under the BS testing regime, during the fire testing of a multi bladed damper, multiple gaps could occur. However, as long as each of these gaps is less than the designated size, the damper will still meet the performance criteria.
In contrast, the European Standard 1366-2 incorporates measures to assess the levels of leakage of hot gases, as well as testing the material of the damper itself.
In addition, due to a change from bead thermocouple to plate thermocouples for furnace control, more heat is required into the furnace to achieve the time/temperature performance. This means the European tests are more difficult to pass.
Depending on how the product performs, it will be categorised under the following criteria:
Performance criteria – after five minutes from start of test.
a) Integrity {E} –Leakage through the fire damper shall not exceed 100l/ (sm2) [corrected to 20°C]. Sustained flaming. Permitting penetration by either 25mm or 150 x 6mm gap gauge.
b) Insulation {I} – Temp criteria defined by BS EN 1361-1 (Rise on average in excess of 140°C above the initial average or at any one location in excess of 180°C above the initial average).
c) Leakage {S} Leakage through the fire damper shall not exceed 55.5 l/(sm2) [corrected to 20°C)
Each product is tested to BSEN 1366-2 1999 and classified to BSEN 13501-3 2005as follows, depending on the tests passed:
E – Integrity
ES – Integrity and smoke
EI – Integrity and insulation
EIS – Integrity, insulation and smoke leakage
A number placed after the letters says how many minutes the fire damper will withstand conditions, for example an EIS90 product will meet the fire integrity, insulation and smoke leakage requirements for an hour and a half.
The fire protection characteristics of an EIS rated product compared with a BS476 will be better due to the reduced transmission of hot gases through the closed damper, and the reduction of temperature rise on the non-incident side of the damper, minimising the chance of flash-over. This is particularly important where fire dampers are fitted in ductwork as there is a risk that dust or debris gathered near the non-incident side of a fire damper could easily combust if there is no control of the heat radiating from neighbouring surfaces.
Product design
All TROX fire dampers tested to EN 1366-2 incorporate a specially-designed layer of insulation material – 40mm thick – which automatically contains the heat, protecting the non-incident side of the damper from the escalation of temperature and leakage of smoke. In comparison with conventional UK fire dampers, there is less radiation of heat through the blades, and the damper seals are designed to prevent hot gas leakage.
Routine maintenance is easier with TROX fire dampers compared with traditional curtain dampers, due to it being possible to maintain them from outside of the ductwork.
TROX supplies both BS and EN classified fire dampers, and is committed to supporting both. We want our customers to be fully aware, however, of the differences between these two classifications before specifying these safety-critical products.
