# The Road Vehicles (Construction and Use) Regulations 1986, Paragraph 6: Protection against flammable conditions


(1) Hydrogen leakage and permeation from the compressed hydrogen storage system must not directly vent into the passenger compartment, or into any enclosed or semi-enclosed spaces within the hydrogen-fuelled vehicle that contain unprotected ignition sources.
(2) Any single failure downstream of the main hydrogen shut-off valve must not result in accumulations in levels of hydrogen concentration in the passenger compartment.
(3) The requirement in sub-paragraph (2) is met if the hydrogen concentration in the passenger compartment does not exceed 1.0% by volume when tested in accordance with sub-paragraph (4).
(4) The test procedure for determining levels of hydrogen concentration in sub-paragraph (2) is the test procedure for integrity of enclosed spaces and detection systems in paragraph 3.2 of Annex 5 to ECE Regulation 134.02.
(5) If, during operation, the hydrogen concentration exceeds 3.0% by volume in the air in the enclosed or semi-enclosed spaces of the hydrogen-fuelled vehicle, a warning must be provided in accordance with paragraph 7.
(6) If, during operation, the hydrogen concentration exceeds 4.0% by volume in the air in the enclosed or semi-enclosed spaces of the hydrogen-fuelled vehicle, the main shut-off valve must be closed to isolate the compressed hydrogen storage system.

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Source: https://www.legislation.gov.uk/uksi/1986/1078/schedule/5A/paragraph/6 (the official version)
Page: https://openlegislation.uk/road-vehicles-construction-and-use-regulations-1986/schedule-5A/paragraph-6
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.