Best Oxygen Deficiency Monitor (updated for 2024)

Oxygen Detector, Oxygen Monitor -

Best Oxygen Deficiency Monitor (updated for 2024)

An oxygen deficiency monitor alarms when oxygen levels in a indoor space go below 19.5%. While maintaining an oxygen level of 20.9% is important, detecting the specific gas responsible for oxygen displacement can be more effective. Gas detectors continuously monitor indoor spaces, alerting occupants when dangerous levels of specific gases are present. Ventilation plays a vital role in maintaining safe air quality. The choice between oxygen deficiency monitors and gas-specific detectors depends on factors such as sensitivity, price, best practices, guidelines, and regulations. Gas-specific detectors offer targeted monitoring, allowing for quick identification and corrective action when harmful gases are detected, ensuring a safer environment.



  • Oxygen Depletion Sensors can save lives in indoor situations
  • OSHA and NIH requires Oxygen Depletion Detectors in certain circumstances
  • Oxygen deficiency monitors are vital for indoor safety and confined spaces.
  • Proper ventilation and limiting oxygen-depleting processes are crucial.
  • Home air quality is best detected with CO2 monitors rather than a oxygen detector
  • Oxygen detectors do not last as long as CO2 monitors.
  • Oxygen detectors are not as sensitive as CO2 monitors
  • Low oxygen (less than 19.5%) is considered unacceptable by OSHA.

Best Oxygen Depletion Alarm and Oxygen Deficiency Monitor

The best Confined Space Gas Detectors are the following:

What is Oxygen Depletion?

    Oxygen depletion in air occurs when the concentration of oxygen in the air decreases, leading to a situation where the risks of human asphyxiation is significant. Asphyxiation is the effect of low oxygen concentration, which can lead to suffocation and death. An atmosphere containing less than 18% oxygen is potentially hazardous, and entry into areas with atmospheres less than 19.5% oxygen is not recommended by OSHA. Asphyxiation due to low oxygen concentrations is often rapid and with no prior warning 

    What is the difference between Oxygen Depletion, Oxygen Deficiency and Oxygen Displacement?

    Oxygen depletion and oxygen deficiency are two very similar concepts. Oxygen depletion refers to a situation where the concentration of oxygen in the air decreases below a certain level, leading to a risk of asphyxiation. This can happen in confined spaces or areas where the air is not properly ventilated, such as underground mines, storage tanks, or silos.

    Oxygen deficiency refers to a situation where the total amount of oxygen in the air is insufficient to sustain life, regardless of the concentration. This can happen at high altitudes, where the air pressure is low, or in areas where the air is contaminated with other gases, such as carbon monoxide or nitrogen.

    There is a third term called oxygen displacement. Oxygen displacement refers to the oxygen level decreasing as a results of another gas entering the volume of space and reducing the % volume concentration of the oxygen.

    Fast and Slow Oxygen Depletion Examples

    There are primarily two situations encountered in asphyxia by gaseous substances. One is the sudden decrease of oxygen in the atmosphere, and the other is the gradual depletion of oxygen gas due to its replacement by another gas.

    FAST Oxygen depletion examples include:

    • (a) carbon dioxide (CO2) or methane (CH4) present in a sewer or in a silo,
    • (b) a methane gas explosion in a mine, and
    • (c) nitrous oxide (N2O), which is used as an anesthetic substance, by the erroneous connection of an N2O tube with an oxygen tube into the anesthetic device

    SLOW Oxygen depletion examples include:

    • Leakage of gases from a cylinder such as freon gas, liquid propane and nitrogen (N2) would slowly displace the oxygen in the air.
    • Oxygen depletion may also occur in a small sealed space, indoor space or tight confined space. Most extreme example is breathing in a plastic bag.

    What is the OSHA limit for oxygen?

    According to the OSHA regulations, an environment with an oxygen concentration below 19.5% is considered oxygen-deficient.

    Low oxygen levels can cause dizziness, shortness of breath, and even unconsciousness or death in extreme cases. Workspaces with an oxygen concentration below this threshold are deemed hazardous and require appropriate safety measures and monitoring systems.

    How does Oxygen Deficiency occur?

    Oxygen deficiency occurs when the concentration of oxygen in an environment falls below the standard 20.9% in indoor air. This reduction in oxygen can be caused by various factors and phenomena. Some examples include:

    • Gas Addition. Displacement of oxygen can happen in spaces with high concentrations of added gases such as nitrogen, carbon dioxide, or other gases. For instance in research and development environments using storage tanks and enclosed spaces can become oxygen-deficient due to a buildup of these gases, thus making the environment hazardous for individuals entering such spaces. Additionally, oxygen can be depleted in environments with poor ventilation, as the oxygen is not being consistently replenished and human exhalation of carbon dioxide can displace the oxygen in the air.
    • Combustion processes also contribute to oxygen deficiency. When fuels such as coal, gasoline, or wood are burned, they consume oxygen to produce energy. In spaces with inadequate ventilation, this consumption can lead to the depletion of oxygen. This is common when people forget to turn off their car in the garage. This is a common issue in confined spaces with limited air circulation, like tunnels, mines, or appliance and boiler rooms.
    • Industrial and manufacturing situations are also prone to oxygen deficient situations. Chemical reactions can create oxygen-deficient environments. When substances such as iron, steel, or other metals rust, they undergo a process called oxidation, which uses up oxygen. Similarly, the decay of organic materials like plants or food in confined spaces can lead to a reduction in oxygen levels.
    • Gas Stratification. Stratification of gas occurs when gases of different densities separate into distinct layers within a container or space. This can create oxygen depletion. For example, carbon dioxide introduced into a confined space with lighter gases can sink to the bottom and displace the lighter gases upwards, creating a stratified oxygen depleted layer of gas. 

        🚀 Fun Fact 🐝

      Did you know that although oxygen makes up about 21% of the air we breathe, it is not evenly distributed throughout the atmosphere? The concentration of oxygen is actually slightly higher at lower altitudes and decreases as you go higher up into the atmosphere. This is why climbers and pilots need to carry supplemental oxygen at high altitudes to avoid altitude sickness and hypoxia.

      What Causes Low Oxygen in the Home?

      Several factors can contribute to low oxygen levels in a home. The primary factors include poor ventilation, combustion of fuels, and human exhalation of carbon dioxide due to tight and or poor fresh air exchange.

      Combustion sources such as gas heaters, fireplaces, heating systems, stoves, or candles, which consume oxygen and release carbon dioxide and other gases will lead to reduced oxygen in the home. Inadequate ventilation can further exacerbate the problem, as fresh air is not brought in to replace the consumed oxygen.

      Poor ventilation can significantly affect the oxygen levels in a house. Modern houses are designed to be energy-efficient, which often results in airtight construction and insulation. Although this helps reduce energy consumption, it can also limit the flow of fresh air into the house. Inadequate ventilation can trap stale air, carbon dioxide, and other contaminants inside the building, leading to a decrease in oxygen levels. Regularly opening windows or taking steps to improve the ventilation system can help combat this problem.

      Human breath CO2 exhalation is also a air quality concern. For a home situation however, poor air quality is mostly caused as a result of low fresh air ventilation (low Air Changes per Hour - ACH), too many people in a small room that builds up the carbon dioxide gas levels from (CO2) exhalation of breath. In this case, a carbon dioxide monitor would be more appropriate, more sensitive and more affordable than using a oxygen monitor to observe a change in air quality.

      What causes Oxygen Deficiency Alarming in Confined Spaces?

      Oxygen deficiency in confined spaces can be caused by several factors, including natural and human activities. 

      Inadequate ventilation or the presence of barriers in confined spaces can contribute to oxygen deficiency by preventing the proper circulation of air. This can cause the oxygen levels to drop below the required threshold for human safety, leading to health risks such as hypoxia, asphyxiation, or even death. 

      One of the primary causes of oxygen deficiency is the consumption of oxygen by living organisms, such as humans, animals, and microorganisms. As these organisms breathe or carry out metabolic processes, they consume oxygen and release carbon dioxide, which in turn reduces the oxygen concentration in the surrounding area. In a confined space, the limited air circulation can exacerbate this issue by preventing fresh air from replacing the depleted oxygen.

      Another cause of oxygen deficiency in confined spaces is the combustion of materials. When fuels like gasoline, diesel, or natural gas are burned, they consume oxygen in the process and produce carbon dioxide, water vapor, and other byproducts. This can lead to a significant drop in the oxygen concentration, especially if the confined space has poor ventilation or if multiple combustion sources are present. An established study on oxygen depletion off the Changjiang (Yangtze River) estuary reveals that the degradation of organic matter could also lead to oxygen deficiency.

      Chemical reactions, either intentional or accidental, can also cause oxygen deficiency. Some chemical reactions, like oxidation and rusting, consume oxygen as a reactant and generate other compounds. In confined spaces, these reactions can rapidly deplete the available oxygen and create hazardous conditions if not adequately controlled or monitored.

      How is Oxygen Deficiency Measured?

      Oxygen deficiency, or low levels of oxygen, can be determined by employing oxygen monitors. These devices typically consist of electrochemical sensors that are sensitive to changes in oxygen levels, typically with a resolution of about 0.1% oxygen. When introduced into an environment, the sensors respond to changes in oxygen concentrations by generating an electrical signal proportional to the oxygen content. This signal is then interpreted and displayed as an oxygen concentration value. 

      What is an Oxygen Depletion Monitor?

      A oxygen depletion monitor detects and measures the oxygen concentration in air. An oxygen depletion monitors is also referred to as a, oxygen detector, oxygen monitor, oxygen depletion alarm, oxygen analyzer, oxygen sensor and oxygen deficiency monitor.

      Most oxygen depletion monitors work by using oxygen sensors that measure the amount of oxygen in the surrounding environment. The sensors send signals to the monitor consistently, and if the levels fall below a predefined set point, the monitor will trigger an alarm or shutdown system to alert individuals or control devices in the area. These alarms can come in various forms, such as flashing lights, sirens, and triggering relays to then turn ON/OFF appliances or valves to assist in corrective measure and reduce damage.

      What is a Confined Space Oxygen Detector?

      A confined space oxygen detector, is the same as a oxygen depletion monitor, but is made for confined space applications. Oxygen levels can drop in confined spaces due to the consumption of oxygen by workers or the presence of other gases that displace oxygen. Low oxygen levels (less than 19.5%) can lead to dizziness, fatigue, and even loss of consciousness. An oxygen detector will sound an alarm if oxygen levels drop below a safe level. A case where CO2 displaced Oxygen in a manhole was investigated by OSHA.

      Importance of Oxygen Deficiency Monitoring

      Oxygen deficiency monitoring plays a crucial role in ensuring the safety and well-being of individuals working in environments where the oxygen concentration may deviate from the standard atmospheric levels. The air we breathe normally contains 20.95% oxygen, which is essential for humans to survive. However, certain work environments, such as laboratories, industrial plants, and confined spaces, may introduce the risk of oxygen depletion due to various factors like the presence of inert gases or nitrogen.

      Oxygen deficiency monitors are devices designed to measure the oxygen concentration in the ambient air and provide a real-time oxygen level readout. When the oxygen levels deviate from the standard 20.95%, these devices trigger an alarm, alerting workers of a potential hazardous atmosphere. The Occupational Safety and Health Administration (OSHA) specifies that a hazardous atmosphere may include one where the oxygen concentration is below 19.5% or above 23.5%.

      In situations where oxygen levels fall below the safe range, humans can experience serious health effects such as shortness of breath, confusion, and even unconsciousness, eventually leading to death by asphyxiation. On the other hand, environments with increased oxygen concentrations pose the risk of fires or explosions. Thus, proper monitoring of oxygen levels is essential for worker safety.

      Many industries use inert gases and nitrogen in their operations, which, if released or leaked, can lead to oxygen-deficient atmospheres. Cryogenic liquids, such as nitrogen, helium, carbon dioxide, nitrous oxide and argon, are widely used across laboratories as they are kept in their liquid state through temperature and pressure applications. These liquids can displace oxygen when released, creating a hazardous low-oxygen environment. Oxygen depletion sensors and oxygen deficiency monitors help detect such situations in real-time and prevent potentially life-threatening consequences.

      How do Oxygen Depletion Monitors work?

      The primary component of an oxygen depletion monitor is an oxygen sensor, which often uses an electrochemical process to measure fluctuations in oxygen concentration. The oxygen sensor is designed to measure chemical reactions created by the electrical output that is proportional to changes in oxygen levels.

      If there is a leakage of stored gases, oxygen depletion monitors detect the lowered oxygen levels and display them on a screen. Consequently, if the oxygen levels drop below the set safety levels, these systems automatically activate alarms to notify the occupants of the room or area. Moreover, some advanced oxygen monitor systems are connected to automated ventilation controls via triggered relays that can restore safe atmospheric conditions when oxygen alarms are triggered.

      CASE STUDY: Oxygen Depletion Monitoring in Cryogenic Work at NIH locations

      Cryogenic liquids are become a critical supply to our modern day high tech medical facilities. These include liquid nitrogen and helium, that are used to store laboratory samples, maintain low temperatures, and preserve superconductivity in medical imaging equipment such as MRI and NMR machines. 

      Cryogenic liquids, upon dispensing, release vapors and gases with varying properties. Nitrogen and helium gases, for example, are colorless, odorless, noncorrosive, nontoxic, and inert. However, they act as simple asphyxiants, meaning they can displace oxygen in the air when present in high concentrations and can be a danger to workers using these cryogenic liquids. Example situation this can occur includes:

      • Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) rooms;
      • Cryogenic/Transmission Electron Microscope (TEM) rooms;
      • Freezer and tank farms;
      • Bulk storage tanks, particularly if kept indoors or outdoors below ground level; and
      • Compressed gas manifold rooms or other compressed gas bulk storage. 

      To prevent injury and oxygen depletion, the National Institute of Health provides guidance on the installation, maintenance, and calibration of oxygen monitoring devices in animal and laboratory areas that are located in all NIH owned and leased buildings.

      NIH requires oxygen monitoring devices to be installed in any indoor location where compressed gases and/or cryogenic liquids are stored and/or dispensed in manner that could create the potential for the displacement of oxygen.

      The installation of the oxygen monitoring device will rely on the manufacturer’s specific requirements and recommendations. Some of these requirements may include, but not be limited to: 

      • Installing the device sensor(s) close to an area where a gas release would most likely occur;
      • Placing the device sensor(s) at the proper height depending on the density of the gas and the simulation of an individual’s breathing zone;
      • Ensuring the device’s display is accessible; and
      • Performing a leak test of the oxygen monitoring device’s sample lines, system components and fittings.  

      How do you measure oxygen levels in the air?

      Oxygen sensors are the core component of oxygen monitors and alarms. They can use different technologies to detect oxygen levels, such as:

      Zirconia Oxygen Sensor - Used in automotive and industrial applications to monitor combustion efficiency and emissions.

        Paramagnetic Oxygen Sensor - Used in medical applications to monitor oxygen levels in blood and respiratory gases.

        Electrochemical Oxygen Sensor - Used in industrial and environmental applications to monitor oxygen levels in air and mostly used in depletion oxygen monitors.

        Infrared Oxygen Sensor - Used in aerospace and industrial applications to monitor oxygen levels in sealed environments.

        Ultrasonic Oxygen Sensor - Used in medical and industrial applications to monitor oxygen levels in liquids and gases.

        Optical Oxygen Sensor - Used in medical and biotechnology applications to measure oxygen levels in tissues and cells.

        In summary, measuring oxygen levels can be achieved using sensors that employ different technologies, such as electrochemical, optical, and ultrasonic sensors. These sensors are integrated into oxygen detectors, monitors, or alarms that provide instant readings and trigger alerts when oxygen levels fall outside the safe range.

        Typical Electrochemical Oxygen Sensor Element

        How can I prevent Oxygen Depletion in a Confined Space?

        One of the most critical aspects of ensuring safety in confined spaces is to prevent oxygen depletion. To achieve this, implement the following measures.

        • Ensure to always monitor the oxygen levels within the confined space. A calibrated gas monitor is essential for accurately determining the oxygen content in the atmosphere. As a rule of thumb, the normal volume of oxygen in the ambient air is 20.9%. Ensure that the alarm levels are set up correctly: 19.5% for oxygen deficiency, 23.5% for oxygen enrichment, and 10% LEL (Lower Explosive Limit) for combustion gases. This monitoring not only prevents oxygen depletion but also ensures prompt and effective response in case of any breaches in oxygen level safety standards.
        • Ensure proper ventilation. Ensuring adequate airflow within the confined space can prevent dangerous build-up of oxygen-depleting substances such as carbon dioxide, nitrogen, and argon. The use of forced-air ventilation systems or exhaust fans can help maintain a safe oxygen concentration.
        • Minimizing the use of oxygen-depleting equipment or processes within the confined space is crucial. Activities like welding, cutting, and brazing can consume oxygen, leading to potential oxygen deficiency. If using such equipment is unavoidable, implement additional safeguards, such as constant monitoring and additional ventilation.
        • Lastly, educate and train employees on the hazards of oxygen depletion, confined spaces, and proper safety protocols. Familiarizing workers with the risks, symptoms, and the appropriate procedures to follow in an emergency will contribute greatly to preventing oxygen depletion in confined spaces.

        confined space

        Does OSHA require that oxygen deficiency monitors be placed in any room where compressed gases are used or stored?

        Yes it does.

        The Occupational Safety and Health Administration (OSHA) does require the installation of oxygen deficiency monitors in rooms where compressed gases are used or stored. These storage areas are often located outdoors or in confined spaces, such as basements or storage closets. The primary purpose of placing oxygen monitors in these areas is to ensure the safety of the people working near these gases and prevent potential hazards due to insufficient oxygen levels or unexpected gas leaks.

        Determining the appropriate number of oxygen monitors and their installation height depends on the layout, size, and ventilation of the space. Although OSHA guidelines do not specifically state the number of monitors required, it is essential to ensure adequate coverage so that possible oxygen level fluctuations are detected in a timely manner. 

        Do I need to Install a Oxygen Deficiency Monitor?

        Some industries and codes mandate the use of Oxygen Deficiency Monitors. Examples include:

        Where Should Oxygen Deficiency Monitors Be Installed?

        OSHA requires that oxygen depletion monitors be placed in a room where compressed gases are used or stored. However, the storage areas of compressed gases are frequently outside or in confined spaces, such as basements or closets. In this case, monitors should be located where a gas manifold or large gas connection or interchange is located. With respect to smaller confined rooms and closet spaces where dewars of gas are stored, the oxygen deficiency monitor should be installed directly in the storage area. 

        Sometimes the rooms where the danger occurs may be isolated and a secondary beacon or alarm system may be needed to be added to prevent dangers from entering and not hearing or seeing a potential enabled alarm. In some cases, the actual physical oxygen monitor should not be located in the room (MRI, NMR) and a physical pumping or aspirator function is required to continuously suck and sample the air from the location and draw the air on the monitor which is typically in an adjacent room.

        How Many Oxygen Deficiency Monitors Do I Need to install? 

        Oxygen monitors are compact, typically not taking up more than 6 inches in height, 6 inches in width and 4 inches in depth (from the wall). So they can be easily mounted in most indoor spaces.

        The exact location depends on the layout and geometry of your indoor space. As vendors, its nearly impossible to tell customers where to place the monitors since we are not on the ground to make a assessment to we have put together some rules of thumb to consider when determining a location for your oxygen depletion monitor:

        • Make sure it can be accessed for maintenance.
        • Make sure it is unlikely to be damaged from foot traffic, trolleys or doors opening and closing.
        • Make sure is it visible to all occupants. For example, if occupants are mostly in the lab on a computer desk, make sure they have visibility to the displays and alarm beacon.
        • Make sure the monitor is placed at about 5ft height. This allows easily access for maintenance. This also best represents the human inhalation oxygen levels. In addition placing it at about 5ft high allows for easy visibility if an alarm was to take place and also easy access to view the actual instantaneous oxygen concentration with a quick glance.
        • Make sure it is in the vicinity (a few feet) to the potential "leakage" source or potential hazard.
        • Make sure there is at least one oxygen depletion monitor per room as required by OSHA.
        • Make sure there is at least one oxygen depletion monitor per 400-800 sq feet if the room is open plan format and as long as there is adequate ventilation for the space as defined by ASHRAE code. If the space has walls, partitions and doors, make sure there is one oxygen depletion monitor per isolated space or room.

        What is the difference between an Oxygen Deficiency Monitor and a Personal Oxygen Detector?

        An Oxygen Deficiency Monitor is made to be fixed mounted (permanently mounted) in a room or confined space for uninterrupted continuously monitoring of the oxygen concentration. While a Personal Oxygen Detector is a portable device used to monitor the oxygen concentration in the immediate vicinity of an individual and usually held by the person or mounted on to them via an alligator or belt clip.

        Which is Better, an Oxygen deficiency monitor or a Carbon Dioxide Monitor?

        In situations like a brewery where a oxygen depleted environment could be caused by a carbon dioxide leak, it is often preferred to monitor the indoor air with a Carbon Dioxide Monitor Alarm in ppm. CO2 sensors are cheaper, last longer and are more sensitive then an equivalent cost Oxygen sensor. For example, a typical CO2 NDIR sensor that costs $100 has a much finer resolution and sensitivity of about 10ppm of carbon dioxide. An equivalent Oxygen sensor for that costs about $1000, has a resolution and sensitivity of about 1,000ppm. So in other words, it is cheaper and better (benefit per cost) to detect CO2 gas than to detect O2 gas. Now this is specific to carbon dioxide gas, and in situations such as CO2 for brewery and CO2 for dry ice, and CO2 for cryogenics, then CO2 continuous safety monitoring is a better more affordable option. 


        Gas detection is crucial for preventing health risks and asphyxiation caused by oxygen depletion. While oxygen deficiency monitors continuously measure O2 levels and trigger alarms for corrective actions, monitoring specific gases like CO2 can be more effective in certain scenarios. Gas detectors, utilizing electrochemical or infrared sensors, identify hazardous atmospheres with oxygen levels below 19.5% or above 23.5%. OSHA mandates their use in confined spaces and areas with compressed gases. Proper ventilation, limiting oxygen-depleting processes, and training workers are essential. Various industries, including laboratories, manufacturing, and healthcare, rely on gas detectors to ensure a safe working environment.

          About The Author

          Dr. Kos Galatsis ("Dr.Koz") is the President of Forensics Detectors where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters, and gas analyzers. He has been designing, building, manufacturing, and testing toxic gas detection systems for over 20 years.

          gas detector expert

          Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Read more about Forensics Detectors here.

          Phone: +1 424-341-3886