A group of workers of the Occupational Health Service have therefore, since the 1986 seminar, worked at collecting the knowledge of substitution that exists in the Occupational Health Services and making this knowledge widely accessible to the workers of the Service. If a trade Occupational Health Service has a principal department and several geographically spread subdepartments, it was only sent to the principal department. In order to substitute, the chemical substance or material which is the cause of the considerations of substitution must be removed from the working process. There is a clear tendency that substances with high vapor hazard ratios (VHRs) that is with low threshold limit values and/or high vapor pressures, are replaced by substances with considerably lower VHR. The rest of the satisfied persons judged the result from toxicity assessments or measurements of pollution.