During the construction phase other potential contaminants, such as cutting oils or cleaning agents used in system construction or subsequent maintenance activities, should be considered.A risk analysis should be performed to determine the likelihood of other contaminants which may be present and to assist with the mitigation of their sources, or the development of testing strategies where applicable. When a system has been verified through sampling and testing to be clean, testing frequencies within the distribution system may be reduced because distribution piping systems prevent the ingress of contaminants. For additional discussion on this matter, refer to the ISPE Good Practice Guide: Process Gases [29].