Atmospheric monitoring is one of the most important parts of safe entry operations for confined spaces. The most lethal hazards historically are problems with the atmosphere.

General Rules for Atmospheric Monitoring

  • Prior to entry

  • Continuously during entry operations

  • Cover all areas of the space where personnel will be working.

Atmospheric monitoring must be completed prior to entering the confined space. In those situations where effective monitoring of the work area cannot be completed prior to entry special procedures must be used. These procedures would typically involve the use of respiratory protection and possibly other special precautions.

Atmospheric monitoring should be continuous during the entry. Anytime there are people in the space the atmosphere should be monitored. The current regulations stop short of clearly requiring continuous monitoring. This point is open to interpretation from a compliance standpoint. From a safety perspective, continuous monitoring is obviously the best choice. Atmospheric conditions may change during the work.

Monitoring must also cover all areas of the space where entrants may be exposed to the hazards of the atmosphere. Continuous monitoring should then be established near the breathing zone of the entrants. Another option in this area is to monitor between the entrants and the most likely source of potential atmospheric problems. This may be an effective option in a situation such as uncontrolled sewer pipes.


The flowchart in Figure 1 illustrates the basic process of atmospheric monitoring. In confined space entry operations there will always be a need for atmospheric monitoring so the first point on the flowchart is automatically "yes". You must then identify the potential atmospheric problems you may encounter. Oxygen and flammability issues should generally be checked as a standard practice. This is the simplest approach to these items because instruments designed for confined space work will usually have both of these sensors. The oxygen sensor may be used in the vast majority of operating environments without specific identification of other issues that may be present. The flammable sensor is typically a broad range sensor that will detect flammability problems without specifically identifying the flammable involved. Acceptable ranges for these materials are general which also simplifies monitoring.

Toxic sensors are most often chemical specific. This requires that potential toxic contaminants be identified specifically prior to being able to select the appropriate monitoring equipment. Each toxic has a specific acceptable level.

After the hazards have been identified the specific monitoring equipment may be selected. Equipment must be selected based on the hazard assessment not availability.

The most effective approach is to calibrate all the monitoring equipment prior to beginning work on the confined space. Manufacturers' recommendations vary on frequency of calibration. The ideal situation is to insure that instruments are calibrated each day of use at the beginning of the shift. At a minimum confirm that all devices have been properly calibrated recently.

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