Confined Space Monitors

Commonly known as the four gas monitor or four gas detector, a confined space monitor is designed to allow technicians to work in areas that could be hazardous due to lack of ventilation. They are defined as having limited openings for entry and exit; unfavorable natural ventilation which could contain or produce dangerous or toxic gas buildup. These spaces are defined as not intended for continuous employee occupancy. There are different classifications of confined space, as defined by NIOSH, and they include:

Confined Space, Class "A": A confined space that presents a situation that is immediately dangerous to life or health (IDLH). These include but are not limited to oxygen deficiency, explosive or flammable atmospheres, and/or concentrations of toxic substances.
Confined Space, Class "B": A confined space that has the potential for causing injury and illness, if preventative measures are not used, but not immediately dangerous to life and health.
Confined Space, Class "C": A confined space in which the potential hazard would not require any special modification of the work procedure.

Section 6-Testing and Monitoring

Entry into a confined space is prohibited until the initial testing of the atmosphere has been done from the outside. Appropriate tests are performed to ensure the atmosphere is safe as long as personnel are present. Monitors should be calibrated in accordance with the manufacturer's guidelines and calibration information should be recorded.