# The Oil Heaters (Safety) Regulations 1977, Paragraph 2


After the heater has been finally adjusted as specified in Appendix C to the British Standard Specification of 1974 it shall be exposed for 5 minutes to a steady frontal horizontal draught at a velocity not exceeding 8 metres per second. During this 5 minute period not more than 10 flashes of flame shall appear outside the heater, none of which shall last as long as one second or exceed 50 millimetres in length.

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Source: https://www.legislation.gov.uk/uksi/1977/167/schedule/3/paragraph/2 (the official version)
Page: https://openlegislation.uk/oil-heaters-safety-regulations-1977/schedule-3/paragraph-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.