This book provides information on the generation and the effects of hazardous substances that are produced during welding and allied processes. These processes are thermal cutting, thermal spraying, soldering and brazing. The book offers guidance on the determination of hazardous substances and it simplifies assessment of the hazard due to hazardous substances. In addition, the book explains tests in order to understand the concentration and intensity of key hazardous substances. Last but not least, the book suggests several possibilities of avoiding the risk to worker’s health as a result of exposing them to these substances.