This standard specifies the health and safety requirements for the design of metering and mixing units for reaction moulding machines. The significant and specific hazards are listed in clause 4 and are dealt with in this standard. This standard does not cover completely the hazards arising from the use of highly flammable additives, for example, pentane used as a blowing agent (see 4.7), because these hazards depend to a large extent on the additives and processes used. This standard does not cover the hazards arising from the assembly of separate units not supplied at the same time by the same manufacturer. This standard does not cover the hazards arising from the movement of powered mixing heads; for these, see EN 1612-2. This standard applies to metering and mixing units manufactured after the date of publication of this standard.