When the oxygen level drops too low in an environment, it can have significant consequences, depending on the context and the specific application. In the case of fuel tank inerting in aerospace, the goal is to reduce the oxygen level to a point where combustion cannot occur. However, if the oxygen level drops too low in other contexts, such as in human-occupied environments or in certain industrial processes, it can lead to various issues.

In Fuel Tanks (Aerospace)

In the context of fuel tank inerting, the objective is to reduce the oxygen concentration to a level that is below the flammability threshold for the fuel. For most hydrocarbon fuels, this threshold is typically around 12% oxygen. When the oxygen level drops below this threshold, the environment becomes non-flammable, preventing combustion even if an ignition source is present.
Ideal Range: For fuel tank inerting, the oxygen concentration is usually reduced to between 5% and 10%. This range ensures that the fuel-air mixture is non-flammable while maintaining a stable and safe environment.
Too Low: If the oxygen level drops significantly below 5%, it may not have any immediate negative impact on the inerting process, but it could indicate a malfunction in the inerting system or an over-injection of nitrogen. This could lead to unnecessary nitrogen consumption and potential inefficiencies.

In Human-Occupied Environments

In environments where humans are present, maintaining a sufficient oxygen level is critical for health and safety. Normal atmospheric air contains about 21% oxygen. If the oxygen level drops too low, it can lead to hypoxia, a condition where the body does not receive enough oxygen to function properly.
Mild Hypoxia (15% - 16% Oxygen): Symptoms may include headaches, dizziness, and shortness of breath.
Moderate Hypoxia (10% - 12% Oxygen): Symptoms can become more severe, including impaired judgment, confusion, and loss of coordination.
Severe Hypoxia (Below 10% Oxygen): This can lead to unconsciousness, brain damage, and even death within minutes.

In Industrial Processes

In industrial settings, certain processes may require controlled oxygen levels for specific reactions or to prevent unwanted combustion. If the oxygen level drops too low, it can:
Impair Chemical Reactions: Some chemical processes require a certain amount of oxygen to proceed. If the oxygen level is too low, the reactions may be incomplete or inefficient.
Affect Combustion Efficiency: In industrial burners or furnaces, a low oxygen level can lead to incomplete combustion, resulting in the production of harmful by-products like carbon monoxide (CO) and unburned hydrocarbons.
Safety Risks: In environments where flammable gases or dusts are present, extremely low oxygen levels can create a false sense of security. If the oxygen level suddenly increases (e.g., due to a leak or ventilation change), the risk of explosion can be higher.