All industrial plants. have processes which require industrial ventilation and exhaust systems to provide a safe working environment from industrial contaminates, which include mists, dusts, fumes, and gases. The safe contamination level which will prevent adverse effects (occupational illness, disability or death) to most workers is defined as the threshold limit value (TLV). The TLV can be based on either 8-hr weighted average, maximum ceiling value, or a short excursion rate. The purpose of the industrial ventilation or exhaust system is to provide an environment (air quality) that is always below the TLV level.

With the passage of the Occupational Safety and Health Act (OSHA) in 1970, the reliability of industrial ventilation systems has become more important to the industrial plant. The present need is for efficiently designed local exhaust systems, which will have a high degree of reliability in meeting the safe environmental levels. However, the need is for a design procedure that is based on accurate airflow theory, and will provide the design engineer with a system which will operate and provide the air quality that is required, without excessive over design of exhaust systems. This over design not only prevents the system from working properly, but the cost in extra energy is wasteful.

One requirement common to many industrial plants is exhaust ventilation for welding operations. This paper is a discussion and analysis of the exhausting of welding fumes and gases. The objective is to analyze the method by which a welding exhaust system fails. Failure means that the welder is exposed to air contamination levels above the TLVs. As an example to be used for the failure analysis of the welding exhaust system, a unique design in a Wisconsin plant was chosen, and the fault tree diagram (FTD) was chosen as a analysis of the welding exhaust system failure.