Hot Work Basics and Wheatstone Bridge Circuit

Hot Work means work involving electric or gas welding, cutting, brazing, grinding, or similar flame or spark producing operations.

An employer shall issue a hot work permit for hot work operations conducted near or on a process. The permit shall document the requirements in 29 CFR 1910.252(a) Fire Prevention and Protection and that they have been implemented before starting work. A hot work permit is intended to control the “Fuel” side of the fire triangle (the other sides of the fire triangle include Oxygen and Heat). Without the Fuel, a fire is not able to start. Fuels shall be removed at least 35 feet away from the hot work site.

Before a hot work permit is issued, it may be necessary to use a combustible gas detector to determine if a fire hazard such as if a flammable gas/vapor is present. Combustible gas instruments work on the principle of catalytic combustion. A Wheatstone Bridge Circuit is contained in the instrument. The Wheatstone Bridge Circuit contains an active filament which heats when a sample gas passes across it with a resultant change in resistance measured by the meter.