Why is E, EW, and EI important when it comes to fire curtains?

Read Time: 4 Minutes

Fire protection in a building is one of the most important considerations for safety. A fire classification system has been designed for barrier products like curtains, doors and glass to describe how effective they are in preventing the spread of a fire. They were developed to be universally understood, regardless of the product. This makes it easier to check a product’s suitability to the needs of your building, which could one day save lives. 

The three fire classifications are: E (integrity rating), EW (integrity and radiation rating), and EI (integrity and insulation rating). Each of them is expressed as a time in minutes, denoting the product’s performance under stipulated test conditions. In this article, we explain how these classifications are determined and what they mean in practice.

E (Integrity)

The most common fire classification is the E or integrity rating. This is a measure of the ability of a construction element that has a separating function (like a fire curtain, door, or shutter) to withstand fire exposure on one side without allowing flames to pass through to the unexposed side.

Integrity is measured by using a furnace to raise the temperature on one side of the product to over 1000°C, following a standardised heating regime (such as that defined in BS EN 1363-1). Three criteria are used to assess the passing of the flame through the barrier:

  • Cracks or openings in excess of a given dimension appear in the product.
  • A cotton pad on the unexposed side ignites.
  • Sustained flaming occurs on the unexposed side.

The test ends when any of these events are observed. Alternatively, a manufacturer can choose to stop the test prior to the flames passing through the product if the desired performance level has been reached. The result is a rating of EXXX, where XXX is the duration of the test in minutes.

Note that there is no measure of the heat passing through the product in an integrity test. That aspect is assessed using the other classifications.

EW (Integrity and Radiation)

In the EW rating, in addition to the integrity being determined as described above, the product’s ability to limit heat radiating from the unexposed side is also measured. This is important for maintaining tenable conditions to allow people time to use escape routes in a building.

During the test, two heat flux meters are placed a distance of 1m from the unexposed side of the product, to measure the thermal energy radiated from the product across a specific area over a given time. One meter is aligned with the centre of the product under test, to measure an average value, while the other is placed to measure what is likely to be the maximum heat flux.

As before, the test is stopped when the integrity fails, or when the measured heat flux exceeds 15 kW/m2 (whichever occurs first).

EI (Integrity and Insulation)

The EI rating is considered as the highest classification level for fire curtains. In addition to the fire integrity described previously, it also assesses the product’s ability to resist the conduction of heat through the material to the unexposed side. This is desirable as it protects anyone standing on the unexposed side from the fire’s heat, and stops any nearby materials from igniting and so spreading the flames.

The insulation rating is the time taken for the unexposed surface of the product to reach a temperature of 140°C above the mean initial temperature before the test began. The test is stopped when this criterion is reached or when the integrity fails (whichever occurs first).

Be sure, be safe, don’t be sorry

To excel in health and safety, for insurance purposes, and to be sure your building can withstand a disaster, the highest classification can make all the difference for your peace of mind. At Adexon, we test to the highest standards and insist on UKAS or equivalent third party certification and CE Marking, to ensure our life-safety products perform in the worst circumstances. We believe that you should insist on these criteria too. Whilst there are minimum requirements in building regulations, superior quality products are always advisable. Fires are unforgiving.

If you want to know more about our excellent fire resistant products and whether they can be used for your building project, please get in touch.

This article was written in November 2022 and updated in April 2023 by the team at Adexon Fire & Smoke.