Safety and performance of heat sensitive devices up to R1 (DN 25) connection size for use on appliances burning 2nd and 3rd family gases with an input rating of 120 kW.Cross References:BS 21BS 903:Part A16BS 1004BS 1179BS 1806BS 2797BS 2871:Part 1BS 2871:Part 2BS 3016BS 3643:Part 3BS 3763BS 3955:Part 3BS 4183BS 4518BS 5057BS 5292BS 5338BS 5494