Proper placement of an oxygen deficiency monitor is an important part of protecting personnel in areas where nitrogen, argon, helium, or other gases may displace the oxygen in ambient air.

While every facility should perform its own hazard assessment, the following guidelines can help when selecting a location for an oxygen deficiency monitor and remote oxygen sensor.

Where Should the Oxygen Sensor Be Located?

Whenever possible, the oxygen sensor should be installed in an area representative of the air personnel are breathing.

For general personnel protection, locating the sensor within the normal occupied or breathing zone can provide a practical indication of oxygen concentration in the surrounding area.

However, the ideal sensor location depends on the specific application. Gas density, potential leak locations, ventilation, and room geometry can all influence how a released gas moves through a space.

For example, a release of cold nitrogen from a cryogenic system may initially remain near floor level because of its low temperature, even though nitrogen at room temperature has a density relatively close to that of air.

For this reason, oxygen monitor placement should not be based solely on whether a displacement gas is considered "heavier" or "lighter" than air.

Consider the Location of the Potential Gas Release

The oxygen sensor should generally be located where it can detect a developing hazardous condition before personnel are exposed.

Consider the location of:

• Cryogenic tanks and dewars
• Gas cylinders and manifolds
• Pressure regulators
• Process equipment
• Gas piping and connections
• Relief valves and vent lines
• Potential leak points

A sensor installed too far from the potential release may not detect a localized oxygen-deficient atmosphere quickly enough.

Consider Room Ventilation and Air Movement

Ventilation can significantly affect oxygen monitor placement.

Avoid installing the oxygen sensor immediately next to:

• Supply-air vents
• Exhaust fans
• Open doors
• Windows
• Areas with unusually high airflow

Strong airflow can expose the sensor to air that is not representative of the surrounding room.

At the same time, areas with limited ventilation or restricted air circulation may allow displaced gases to accumulate. Room layout, partitions, equipment and enclosed spaces should therefore be considered when selecting monitoring locations.

Monitor the Occupied Space -- Not Just the Gas Source

The purpose of an oxygen deficiency monitor is ultimately to protect personnel.

While placing a sensor near a potential gas release can provide early detection, it is also important to consider where employees normally work, enter, or travel.

Large rooms or facilities containing multiple potential release points may require more than one oxygen sensor or monitor to provide appropriate coverage.

There is no universal square-footage rule that determines the correct number of oxygen monitors for every facility. The quantity and location should be based on the potential release, room configuration, ventilation, and facility hazard assessment.

Keep the Monitor Visible and Accessible

When possible, install the oxygen deficiency monitor where personnel can easily see the display and alarm indicators.

The monitor should also remain accessible for:

• Routine inspection
• Sensor replacement
• Calibration
• Alarm testing
• Preventive maintenance

If the ideal sensor location is different from the ideal location for the display, a monitor equipped with a remote oxygen sensor can allow the sensor and user interface to be installed in separate locations.

Consider Alarm Location

Personnel should be able to recognize an oxygen alarm before entering or while occupying a potentially hazardous area.

Depending on the facility, this may include local audible and visual alarms as well as remote alarm devices located outside the monitored room.

Alarm relays may also be used to interface the oxygen monitor with external equipment such as:

• Building management systems
• Ventilation systems
• Remote annunciators
• Warning beacons
• Facility alarm systems

The appropriate alarm strategy should be determined as part of the facility's overall safety plan.

Do Not Install the Sensor in an Enclosed Cabinet

Unless the application specifically requires monitoring inside an enclosure, the oxygen sensor should remain exposed to the ambient atmosphere being monitored.

Installing the sensor inside an electrical cabinet, equipment enclosure, or other restricted space can prevent it from accurately representing the oxygen concentration in the occupied area.