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03 June 2024

European Fire Resistance Standard for Chimneys

Author – Jason Lee, Technical Sales & Engineering Manager.

With the introduction of EN1366-13, chimneys now have an official test to assess the fire resistance of both the product and penetration components when passing through a fire rated compartment wall / floor etc.  Although EN1366-13 is a test standard, it is important that the test results are classified in accordance with the latest revision of EN13501-2, allowing specifiers to correctly assess the fire resistance classification of the product required for the project.

Both SFL Flue & Chimneys residential and commercial Europa Plus and Nova (100-350) systems are tested to EN1366-13.

Historically, in respect to chimneys, there has not been a specific standard in the United Kingdom or in that matter, Europe, that specifically covered the fire resistance of both the chimney construction and associated fire-stopping penetration arrangements when passing through a fire rated compartment wall or floor.  In lieu of this, most manufactures in the UK have either undertaken an ad-hock test, based on the general requirements of BS476 Part 20 or more correctly tested to BS 476 Part 24, Method for the determination of the fire resistance of ventilation ducts, as the only viable alternative.  Unlike today, the main criteria when assessing a chimney for fire resistance was the stability and integrity of the product.  Vary rarely was the insulation performance and hence the surface temperature of the chimney considered.  Failure to observe this could lead to a fire on the un-exposed side, should combustible materials come within proximity to the surface of the penetration and chimney components.  This all changes with the European system that focuses on both the integrity and insulation performance of the chimney system, under the EI classification.

Since 2004 and to date, the European Committee for Standardisation has approved thirteen standards covering fire resistance tests for service installations under EN 1366.  EN1366 Part 13 corrects this historic void and introduces a specific fire resistance test for chimneys and penetration elements as part of a chimney construction under standardised fire conditions.  This standard has now been adopted in the UK under BS EN 1366-13.

In essence, EN1366-13 is very similar to that of BS476 Part 24; however, with one significant difference.  Unlike ventilation ducts, which in the main transport air to different parts of the building, a chimney carries products of combustion from source to atmosphere at high temperature.  EN1366-13 introduces a pre-treatment requirement to simulate the aging that the chimney can suffer over time due to its normal operation.  The pre-treatment involves subjecting the chimney to a flue gas temperature equal to the test temperature based on the manufacturers declared temperature classification for a period of six hours.  As an example, a chimney CE Marked to EN1856-1 with a temperature classification of T600 would require a pre-treatment temperature of 700°C for six hours, before the commencement of the actual fire resistance testing.

This is an important factor above and beyond testing ventilation ducts, as the extended high operating temperatures over the life of the chimney product could affect the performance of the insulation or the integrity of the product, ultimately putting its declared fire resistance at risk.

Key Parts of the Fire Resistance Testing to EN 1366-13

Test Configurations:

The test offers two configurations, one being vertical (EI xxx v_e) and the other being horizontal (EI xxx v_o).

In most cases, as chimney routes are rarely horizontal or vertical, manufacturers test to both configurations and use the lower value of the two tests in their overall fire resistance classification.

In both tests, the chimney is engulfed within the furnace and passes through the fire rated partition wall using the manufacturers penetration components and continues externally in accordance with the distances detailed within the standard.

Fire Tests:

Within the standard there is the option to simulate two fire test conditions:

Fire Test – Type A (i → o):

This test simulates an internal fire through the compartment wall.  The chimney is tested with no openings, so that the internal of the chimney is isolated from the fire.  Assessing the chimney to an external fire within the compartment would be normal, as unlike ventilation ducts, that tend to have discharge grills, chimneys inevitably do not have openings within their construction.

Fire Test – Type B (i → o) (o → i)

In this test the chimney is still engulfed within the furnace; however, an opening is required in the chimney, allowing the fire in the furnace to enter the chimney system, and be drawn through the specimen to atmosphere.  As above, it would be very rare to adopt this test for chimneys; however, there may be exceptional cases where such a requirement may be required.  Currently Building Regulations Part B require the fire resistance test to be conducted externally as per the Type A test configuration.

Performance Criteria:

The performance assessment of the test is effectively the amount of time in minutes it takes for either the integrity, insulation, or both to fail the conditions of the test.  With a Type A test, the insulation performance is a little confusing, as fire is not transmitted into the chimney.  That said, the conduction of heat along the outer case from inside the furnace, passing across the fire rated compartment, together with other forms of heat transfer, must be assessed to ensure that the surfaces on the external chimney and penetration components passing through the fire compartment wall / floor are kept within the limits of the standard.

Integrity (E):

This is the ability of both the chimney and associated penetration components to contain the passage of flames and hot gasses from the exposed side of the fire compartment wall / floor to the unexposed side.  This is assessed periodically throughout the test using gap gauges and cotton pads.  During the test, gap gauges and cotton pads are used to assess the integrity of the chimney as follows:

1. weather a 6mm gap gauge can be passed through the test specimen, such that the gauge projects into the furnace, and can be moved 150mm along the gap; or
2. whether the 25mm gap gauge can pass through the test specimen such that the gauge projects into the furnace
3. a cotton pad does not ignite when placed against the surface of the specimen or area of concern, such as a gap after a period of 30 seconds. 

Insulation (I):

The insulation performance is measured using thermocouples located both on the surface of the penetration components and the chimney passing through the fire compartment wall / floor as detailed within the standard.  The criteria for insulation failure are as follows:

1. increase in the average temperature above the initial average temperature by more than 140 K, or
2. increase at any location (including the roving thermocouple) above the initial average temperature by more than 180 K.

In most cases the integrity and insulation are used together when classifying the fire resistance of the chimney, along with the duration, e.g. EI90, EI120 etc.; however, the classification when considering both insulation and integrity falls to the lowest value.  If claiming an EI classification and the insulation fails at 90 minutes but the integrity fails at 120 minutes, then the classification would be EI90.  It is possible to classify only the integrity; however, most building codes require the full EI classification when considering fire resistance.

Revisiting the Type B fire test:

Although we have discussed that the assessment of a fire as detailed by Type B (o → i) (i → o) in EN1366-13 is very rare for a chimney system, there is a provision within EN1856-1 to cover a fire propagating from the inside of the chimney.  As an example, EN 1856-1 covering metal System Chimneys has a performance classification covering soot fire resistance together with the declared distance to combustible material.  This is classified as Gxx, where xx is the distance to combustibles.  During this test, the chimney is subjected to a soot fire simulation, this requires the chimney to be subjected to a flue gas temperature of 1000°C for 30 minutes.  During this time, no combustible surface must exceed a temperature of 100°C when related to an ambient temperature of 20°C.

In the 2023 revision of the classification standard BS EN 13501-2 Fire classification of construction products and building elements, the soot fire classification has now been added for the classification of chimneys tested to BS EN 1366-13.  In the revision along with the specification criteria of BS EN 1366-13, the soot fire resistance is also now added with the title ‘Fire resistance internal to external’.