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Satisfactory operation of the synchrotron radiation source (SRS) at Daresbury Laboratory depends upon effective cleaning of the stainless steel vacuum vessels and other components. Pursuant to the Montreal protocol, current and proposed changes to European community environmental protection legislation require a reappraisal of all cleaning processes, since many involve chemicals that have been identified as environmentally unfriendly. This article reviews work carried out at Daresbury to establish replacement cleaning recipes for the preparation of stainless steel surfaces for ultrahigh vacuum systems. The importance of achieving clean ultrahigh vacuum for the Daresbury SRS, and environmental considerations in reaching the required level of cleanliness are discussed. Suitable criteria for comparing various cleaning agents are established, based on outgassing rates and stimulated desorption coefficients. Outgassing rates and some partial pressure comparisons are presented here. These demonstrate that the standard procedure used at Daresbury has been chosen with some care in the past. Further work is required before a fully satisfactory alternative procedure can be determined.

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