Oxygen Depletion Alarm: Monitoring Oxygen Deficiency in Enclosed Spaces

A fixed oxygen depletion alarm or oxygen deficiency monitor is an oxygen sensor that constantly monitors a defined space, can control third party systems, and can audibly and visually indicate an incident. The oxygen sensor continually monitors the oxygen level in the enclosed area. If the oxygen level in the air drops below a preset value, the alarm warns occupants both inside and outside the room of the incident.  

Oxygen deficiency monitors or depletion alarms are critical in any room or enclosed area in which low oxygen levels can occur.

Background: Oxygen Levels in Air

By volume, dry air contains 78.09% nitrogen, 20.95% oxygen 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.

At normal temperatures and pressures, 20.9% oxygen in the air is considered optimal for humans. When oxygen levels drop below 19.5% hypoxia (lowered oxygen levels) begins to occur. The air is considered oxygen-deficient, although it is still relatively safe for short periods of time or for people who have acclimated their bodies to lower oxygen levels.

Oxygen deficiency at levels below 16% is dangerous for human life. The challenge is that the difference between 16% and 21% is typically made up of inert, odorless gases like nitrogen, argon or carbon dioxide, so the oxygen deficiency may not be noticed immediately. If oxygen levels remain low, sudden unconsciousness or death without symptoms may occur.

Oxygen Deficiency Alarm with Remote Sensor 

To warn occupants of oxygen depletion in an enclosed area or room, oxygen deficiency monitors are used. These include two components:

  • An oxygen sensor housed in a case with audible and visual alarms to warn occupants in the confined space
  • One or more remote monitors with duplicate audible and visual alarms to warn personnel outside the space and before entering the room

The two components are linked by a cable that sends the oxygen level data and power from the monitor to the remote display in real time. Typically a wireless connection is avoided as problems with networks and interference from building materials like concrete and steel render the system useless.

In addition to the sensor and remote display(s), a data link can be made utilizing the devices 4-20 ma output between the sensor and a control panel or dashboard to warn offsite personnel if an oxygen depletion alarm has occurred.

Where are Oxygen Deficiency Monitors Used?

Oxygen alarms are necessary in any place where low oxygen levels can occur. While most people think of a closed environment like an airplane or submarine, a much more common example is a room where pressurized cylinders/tanks of hydrogen, helium, argon, or nitrogen are utilized or stored. If one of the cylinders/tanks, hoses or fittings leak, the rapid outflow of gas can lower the oxygen level in an enclosed area or room rapidly.  

Note that oxygen displacement monitors should not be used to measure for CO2 accumulation.  These gases should be monitored independently of each other. 

Examples include:

  • Hospitals that use gases like nitrous oxide or nitrogen
  • Testing labs that use helium to cool MRI machines
  • Laboratories that use liquid nitrogen, helium or argon for cryo-biology, IVF, cryosurgery or other types of cryogenic research
  • Food production facilities that use liquid nitrogen to package meats, fruits, or dairy
  • Industrial facilities that use argon or other shield gases for welding
  • Factories that use sealed AM machines or 3D printers
  • Diving supply shops that mix gases to refill SCUBA tanks
  • Technology centers that use argon or other inert gases for fire suppression

OSHA Requirements for Oxygen Depletion Alarms

OSHA's 29 CFR 1910.146, "Permit Required Confined Spaces," contains the requirements for practices and procedures to protect employees in general industry from the hazards of entry into permit-required confined spaces.

The standard defines an oxygen-deficient atmosphere as any atmosphere containing less than 19.5 percent oxygen by volume. Any atmosphere that contains less than 19.5 percent oxygen is hazardous and may not be entered by unprotected workers.

The device alarm and warning levels should be where the oxygen concentration is below 19.5% or above 23.5% oxygen concentration levels.

NIH Oxygen Monitoring Devices Protocols

While not law or an OSHA regulation, the National Institutes of Health Protocol for use and maintenance of Oxygen Monitoring Devices has been established to provide guidance on the installation, maintenance, and calibration of oxygen monitoring devices in animal and laboratory areas in all NIH owned and leased buildings. It states:

"An oxygen monitoring device shall be installed in any indoor location where compressed gases or cryogenic liquids are stored and/or dispensed in manner that could create the potential for the displacement of oxygen. At a minimum, the following factors should be used in determining if a device should be installed: manufacturer (e.g., magnet) guidance, volume of gas used, location of gas, and air changes/hour in the room/area. The 2008 NIH DRM notes that both ‘carbon dioxide manifold rooms… [and] nitrogen holding rooms and shall include oxygen level monitoring alarms’ (section 8, pages 8-80). Additionally, compressed gases or cryogenic liquids shall not be located or dispensed in any indoor location that does not have proper ventilation."

Selecting an Oxygen Deficiency Monitor

CO2Meter offers two models of room oxygen deficiency monitors:

  1. Oxygen deficiency only - used near stored or bulk inert gases
  2. Oxygen deficiency plus high carbon dioxide level - use around bulk CO2 storage systems

Both offer separate sensor and monitor units, high-visibility strobe add-on kits, and the ability to daisy-chain up to 3 remote displays.

The sensor modules are hard-wired to the remote display units via Ethernet cable to ensure that a WiFi or network failure does not disable the alarm.

For added precaution, the alarms can be hard-wired into a building-wide 24V power system to minimize power interruptions.

Where Should Oxygen Depletion Alarms be Located?

All gases have molecular weight, but the periodic chart of elements shows us that not all gases weight the same. This is why a helium balloon floats! While oxygen is lighter than normal air, it is not lighter than all gases. Gases that are lighter than oxygen will push the oxygen down to the floor and out of the enclosed space, while heavier gases will push it toward the ceiling.

This chart lists the most common stored gases by molecular weight, with the lightest gases on top and the heaviest gases on the bottom. The lighter the stored gas that may displace the oxygen in a room, the higher the oxygen depletion alarm should be mounted on a wall.

oxygen mole weight

Remote Oxygen Depletion Safety Alarm

Oxygen Deficiency Alarm for Low Temperatures

Our Remote Oxygen Deficiency Alarm for Low Temperatures is designed to protect customers and workers near stored inert gases like Nitrogen, Argon, Helium, nitrous oxide, welding gases and more.

This oxygen monitor alarm has both audible and visual alarms. 3 built-in relays are triggered at 19%, 17%, and 15% respectively that can control an exhaust fan or send an alarm to the fire department or monitoring company. The alarm levels are user configurable to allow for specific applications.

Personal Oxygen Safety Monitor

For industries that require an alternative adjunct to the Remote Oxygen Depletion Safety Alarms, CO2Meter offers a Personal Oxygen Safety Monitor (SAN-20).

The SAN-20 is designed specifically for employees who work in enclosed areas where oxygen depletion may cause personal harm or asphyxiation. 

The Personal Oxygen Safety Monitor, features a man down alarm that is triggered when an employee fall occurs, audible/visual alarms and a vigorous vibration. 

The need for monitoring Oxygen levels in a room can be critical for those working and handling the gas type, and CO2Meter strives in being able to provide fixed and personal devices, that continue to save lives today. 

For more information on Oxygen Depletion Monitoring and selecting the proper monitoring device, contact us today.





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