Fire Protection in Buildings: Understanding Fire Classifications

Fire protection is a fundamental aspect of building safety and regulatory compliance. Fire classification systems have been developed for barrier products such as curtains, doors, and fire-resistant glazing to describe how effectively they limit the spread of fire. These classifications are standardised and product-agnostic, enabling designers and regulators to assess suitability with confidence. 

By providing a consistent method of performance comparison, the system supports informed specification and compliance with fire strategies. When correctly applied, it plays a vital role in protecting life and property. 

The three recognised fire classifications are E (integrity), EW (integrity and radiation), and EI (integrity and insulation). Each rating is expressed as a time in minutes and represents performance under controlled, standardised test conditions. The following sections explain how each classification is determined and how they should be interpreted in practice. 

E (Integrity) 

The E classification, also known as the integrity rating, is the most commonly specified fire performance level. It measures the ability of a separating element such as a fire curtain, door or shutter to withstand fire exposure on one side without allowing flames or hot gases to pass through to the unexposed side. 

Testing is carried out using a furnace to raise the temperature on the fire-exposed side in excess of 1000°C, following a standard heating curve. 

The test is terminated if there’s the formation of cracks or openings that exceed specified limits or sustained flaming on the unexposed side. Alternatively, the manufacturer may elect to stop the test once the required performance duration has been achieved. 

It is important to note that an integrity test does not measure the transfer of heat through the product. This is addressed under the EW and EI classifications. 

EW (Integrity and Radiation) 

The EW classification builds upon the integrity test by also assessing the product’s ability to limit radiant heat transfer from the unexposed side. This is particularly important for maintaining tenable conditions in adjacent spaces and along escape routes. 

During testing, two heat flux meters are positioned one metre from the unexposed face of the product. These instruments measure the thermal energy radiated across a defined area over time. One sensor is aligned with the centre of the specimen to determine an average heat flux, while the second is positioned to capture the maximum expected value. 

The limits for radiation are exceeded once the radiometre exceeds 15kW/m2. The test is not concluded when the radiation exceeds 15kw/m2. The integrity test can continue providing no sustained flaming or gaps. 

EI (Integrity and Insulation) 

The EI classification is often required where fire separation must also limit heat transfer. In addition to maintaining integrity, the product must show no surface temperature increase on the unexposed side of the test specimen. 

This characteristic is critical where occupants, escape routes, or combustible materials are located close to the barrier. By restricting temperature rise, the risk of secondary ignition and heat-related injury is significantly reduced. 

Insulation performance is measured by monitoring the temperature on the unexposed surface. The test is terminated when this surface reaches a temperature of 140°C above the mean initial temperature recorded before the test, or when integrity failure occurs. Similarly to the EW classification, if the criteria for insulation is exceeded, the fire test can continue providing there is no sustained flaming or gaps. 

Applying Classifications in the Correct Context 

Fire classifications provide a common language for describing the performance of fire-resisting barriers and are essential to informed specification and regulatory approval. However, it is critical that these classifications are interpreted in the context of the product type and the applicable standards. 

While the EI classification includes an insulation criterion, it is important to recognise that insulation performance is not a requirement for fire curtains under current UK guidance. BS 8524-1 and BS 8524-2 confirm that fire curtain barrier assemblies replace static partitions and therefore must descend within a clear space. Therefore, the problems of surface temperatures do not apply, but integrity, radiation, and occupant tenability are still relevant. BS 8524-2 further contains data within Tables B1 and B2 which indicates the performance criteria required from a fire curtain to achieve the requisite tenability. 

For this reason, specifying an EI performance for a fire curtain is neither expected nor representative of how these systems are designed or tested in practice. Instead, fire curtains should be selected and assessed against the appropriate E or EW classifications, in line with the building fire strategy and the relevant standards. 

Understanding the distinction between classification systems and product-specific performance requirements is essential for architects, fire engineers, and building control professionals. Correct interpretation ensures that fire curtains are specified for what they are designed to achieve, avoiding inappropriate expectations while maintaining robust life safety performance.