For all IDLH entry, how many employees must be located outside an IDLH atmosphere?

Environments containing IDLH atmospheres are frequently well-enough understood and controlled that a single standby person is adequate. In most fixed workplaces, the atmosphere is known (i.e., has been well defined either through analysis of monitoring results or through a process hazard analysis). In many industrial IDLH situations, only one respirator user is exposed to the IDLH atmosphere at a time, which means that a single standby person can easily monitor that employee’s status (when needed, the standard requires more than one employee outside).

Even in situations where more than one respirator user is inside an IDLH atmosphere, a single standby person can often provide adequate communication and support. For example, in a small pump room or shed, even though two or three employees may be inside an IDLH atmosphere performing routine maintenance activities such as changing pump seals, one standby person can observe and communicate with all of them. In this type of situation, one standby person is adequate and appropriate, as long as the employee(s) outside is able to perform an effective rescue.