EN 3-7 Dielectric test
1. Scope
This Fact File aims to explain the regulations, standards, and codes of practice relating to the use of water-based fire extinguishers on live electrical equipment.
2. Background -Standards/ Regulations/Codes of Practice
The BS EN 3-7:2000+A1 Dielectric test is an optional test for water-based extinguishers which establishes the suitability of water-based extinguishers to be used on live electrical fires and is compulsory for extinguishers to have an F Class rating. (cooking oil fires)
Clause 9 of BS EN 3-7:2000+A1 Dielectric test for water- based extinguishers
9.1 states “The dielectric test is designed to establish the suitability of water-based extinguishers for use on live electrical equipment by measurement of the electrical conductivity of the discharge stream.
In order to be usable on live electrical equipment, water-based extinguishers shall conform to 9.2 “
Clause 9.2 sets out the required performance and says the test shall be in accordance with Annex C
Annex C describes the apparatus and procedure for the test. See Annex A.
The test is optional for the manufacturer but there is a marking requirement to show if it has passed or not passed the test.
16.2 Marking
Portable fire extinguishers using water or foam and not tested to, or not meeting the requirements of clause 9, shall be marked with the following warning: “WARNING: Do not use on live electrical equipment.”
Portable fire extinguishers using other agents and water-based extinguishers meeting the requirements of clause 9 shall be marked to indicate that they are suitable for use on live electrical equipment e.g. “suitable for use on live electrical equipment up to 1000 V at a distance of 1 m.”
NOTE Attention is drawn to national regulations and practice.
In the United Kingdom there are no national regulations regarding the marking of water-based extinguishers on live electrical equipment and there is no statement on the marking or a national practice, therefore the requirements of BS EN 3-7 apply.
3. History
In 1937 The English Electric Company carried a series of tests on behalf of a UK extinguisher manufacturer, to determine if the jet from a foam extinguisher “could be directed on high voltage electrical appliances without risk of shock to the operator of the extinguisher”. The result of the tests “indicated that there was no conduction of electricity through the jet of extinguishing material at the voltage stated The report can be found here
Manufacturers from the 1930’s onwards indicated water extinguishers having a capability to be used on live electrical equipment and the test entered in the British standard prior to the EN standard, BS 5423: 1987 includes a dielectric test for conductivity- 4.7.4 and Appendix J.
BS EN 3-2 Clause 4 covers the dielectric test which it says, “is designed to establish the suitability of water-based extinguishers for use on live electrical installations by measurement of the electrical conductivity of the discharge stream”, The test is described in Annex A.
Subsequently BS EN 3-2 was replaced by BS EN 3-7.
The test in BS EN 3-7 is also used in BS EN 1866-1:2007 Mobile fire extinguisher- clause 7.3 and BS 6165:2019+A1:2022 clause 7.7.2 Small single use fire extinguisher, to allow the use of water-based media on live electrical installations. The test is, therefore, applicable for extinguishers both large and small.
BS 5306-0:2020 in clause 15 “Electricity and fire fighting” discusses concerns about use of fire fighting media, including water on electrical equipment.
4. Conclusion
The dielectric test in BS EN 3-7 is a test to show that an extinguisher tested has suitability for use on live electrical equipment, by measurement of the electrical conductivity of the discharge stream up to a voltage of 35,000 Volts and extinguishers that have passed that test are marked accordance with clause 16.2
5. References
BS 5306-0: 2020 Fire protection installations and equipment on premises Part 0: Guide for selection, use and application of fixed firefighting systems and other types of fire equipment. - BSI
BS EN 3-7: 2004 +A1 2007 Portable fire extinguishers Part 7: Characteristics, performance requirements and test methods – BSI
BS 6165:2019+A1:2022
BS EN 1866-1:2007 Mobile fire extinguishers Part 1: Characteristics, performance and test methods
