Inerting Explained: How to Control Explosion Risks with Inert Gases
Explosions are a major risk in many industries. Companies in the chemical, petrochemical and fine chemical industries in particular work with flammable gases, vapors and substances on a daily basis. In many processes it is not possible to avoid these substances or to always keep them below safe concentrations. That is why inerting is often the only way to prevent explosions and avoid the formation of an explosive mixture.
But, inerting does more than just prevent explosions. It also prevents unwanted chemical reactions, unwanted combustion, oxidation, discoloration and moisture absorption by sensitive products and sensitive materials. In addition, it ensures a safe working environment during maintenance, especially in confined spaces where oxygen levels must be controlled.
In this blog, we explain what inerting is, when it is necessary, which techniques are used and how it fits within the ATEX regulations.
What is inerting?
Inertization, also known as inerting, is the process of lowering the oxygen concentration in an enclosed space by adding an inert gas such as nitrogen, carbon dioxide or argon. The goal is to prevent an explosive atmosphere, prevent unwanted combustion, and protect sensitive products from oxygen and moisture.
Combustible substances can only ignite if there is sufficient oxygen present to sustain combustion. Every mixture of combustible substance, air and inerting gas has a critical oxygen value, the Limiting Oxygen Concentration (LOC). Ignition is impossible below this value. For gases and solvents, the LOC is usually between 8–10% oxygen, for dust explosions between 10–14%.
When is inerting necessary?
Inerting is necessary when explosion risks cannot be eliminated in other ways.
Eliminating fuel is often not possible.
Sometimes flammable substances can be replaced by less flammable alternatives. But in many processes, such as in the chemical and pharmaceutical industry, flammable gases, liquids or substances are simply essential. In the case of liquids, working below the flash point can be a solution, but this is not always feasible. Inerting gas is then introduced to displace oxygen and control the risk.
Working outside the flammable range is often unreliable
Another method is to ensure that the concentration of flammable substance always remains below the explosive limit values. For example, by using ventilation to keep the concentration below the Lower Explosive Limit (LEL). But in practice, this is often not guaranteed. With dust, accumulation can still lead to an explosive mixture.
Inertization is the only workable solution
If fuel cannot be avoided and concentrations cannot be reliably kept under control, inerting is the only effective method. This is not only to prevent explosions, but also to:
• Avoid undesirable reactions with oxygen or moisture.
• Protect product quality (against discoloration, polymerization or oxidation).
• To carry out safe maintenance on installations and pipes.
Applications of inertization
Inertization is used in all kinds of processes where flammable substances or sensitive products are present. The most important applications are:
• Storage tanks and barrels: To prevent flammable vapors from forming an explosive mixture.
• Reactors and mixing tanks: To prevent unwanted reactions with oxygen or moisture.
• Pipes and pipelines: For the safe transportation of flammable liquids and gases, where inerting systems maintain safety.
• Drying installations and silos: To protect powders and solids from moisture and oxidation.
• Centrifuges and filters: For the safe separation and cleaning of substances.
• Comminution and mixing equipment: To prevent dust explosions during the reduction and mixing of powders.
• Loading systems and unloading points: Where explosive mixtures can occur during loading or unloading.
• Maintenance of equipment and pipes: To enable working in an oxygen-free confined space during inspection or repair.
Inerting is not only used to prevent explosions, but also to maintain product quality and to enable safe working during maintenance, while controlling oxygen levels and potential hazards.
Inertization techniques
Inertization is a collective term for various techniques, depending on the application. The three main methods are:
Purging
In purging, an inert gas is used to expel air or process gas from pipes, tanks or equipment. This is often done before start-up or maintenance. The aim is to ensure that no flammable atmosphere or explosive mixture remains.
Blanketing
Blanketing means maintaining a continuous layer of inert gas above a liquid or product, for example in a storage tank. This prevents contact with oxygen or moisture and protects against explosions, discoloration, polymerization or other undesirable reactions. The inerting system monitors flow and pressure.
Sparging
In sparging, inert gas is passed through a liquid in small bubbles. This removes oxygen or other unwanted gases from the liquid. This is used, for example, to strip oxygen from oil or wastewater.
Each technique has its own application, but the goal remains the same: to keep oxygen and sometimes moisture away from flammable or sensitive substances and prevent unwanted combustion.
Choice of Inert Gas
Not every inert gas is suitable for every application. In most cases, nitrogen (N₂) is used. It is cheap, versatile and widely available. In some situations, carbon dioxide (CO₂) or argon (Ar) are used.
Nitrogen (N₂)
• Versatile and cost-efficient.
• Lighter than air (relative density: 0.97).
• Non-reactive, non-flammable.
• Low solubility in water (20 mg/l).
• Available as a gas (300 bar) or liquid (-196°C).
Carbon dioxide (CO₂)
• Heavier than air (relative density: 1.52).
• Also extinguishes fires (used in waste bunkers and silos).
• High solubility in water (2,000 mg/l).
• Can build up a static charge when injected quickly.
• Available as a gas (55 bar), liquid (-20°C), or as dry ice (-78.5°C).
Argon (Ar)
• Completely inert, no chemical reactions.
• Heavier than air (relative density: 1.38).
• Sometimes used in the food industry because it remains in the tank after opening.
• More expensive than nitrogen and CO₂.
• Available as gas (300 bar) or liquid (-183°C).
Limiting Oxygen Concentration (LOC): The Critical Value
The Limiting Oxygen Concentration (LOC) is the maximum amount of oxygen at which a combustible mixture can no longer ignite. This is the most important parameter in inerting. As soon as the oxygen drops below the LOC, an explosion is no longer possible, regardless of how much combustible material is present that could otherwise sustain combustion.
The LOC depends on:
• The type of fuel.
• The inert gas used (e.g. nitrogen or carbon dioxide).
Carbon dioxide (CO₂) is less effective than nitrogen: the LOC for CO₂ is often 25% higher, which means that more oxygen can be present before combustion stops. Therefore, the oxygen volume fraction becomes a critical factor when designing inerting systems that rely on CO₂ as inerting gas.
Examples of LOC values (vol.%):
In practice, an extra safety margin is taken. The operational oxygen limit (MAOC) is often kept 2–4% below the LOC to ensure safe conditions and avoid potential hazards associated with variations in oxygen levels during operation.
The exact LOC value must always be determined experimentally, as it can vary from situation to situation, especially when dealing with complex gas mixtures or fuel tanks in dynamic industrial environments such as the chemical industry and pharmaceutical industry.
ATEX and inertization
Inertization is not an official protection system according to the ATEX directive 2014/34/EU. Nevertheless, it plays an important role within ATEX zones.
When a process involves flammable substances, the area is classified as an explosive zone (Zone 0, 1, 2, 20, 21, 22). Inerting can lower the oxygen concentration below the Lower Explosive Limit (LEL), drastically reducing the risk of explosion and forming part of a broader inerting system designed to prevent ignition sources.
Inerting can therefore lead to a lower zone classification. For example:
• From Zone 20 to Zone 21.
• Or from Zone 21 to Zone 22.
This means less stringent requirements for equipment and installation in fuel tanks, storage areas, or confined spaces. For example, if inerting reduces a Zone 1 area to Zone 2, more cost-effective equipment can be used, such as the Armadex Ex UAP-AC-PRO, suitable for Zone 2 or 22.
However, it is important to note that the inert atmosphere is not always fully guaranteed. Therefore, additional safety measures are still necessary, such as:
• Continuous oxygen monitoring to control oxygen levels.
• Alarm and backup systems in case the inerting gas supply fails.
In short: inerting helps to reduce the risk of explosion in ATEX environments but does not release a company from the duty to comply with ATEX. The presence of inert gases like nitrogen or argon must be constantly monitored to prevent failures that could lead to an explosive mixture.
Risks and safety measures
Although inerting prevents explosions, it also carries risks.
Asphyxiation
The greatest danger is oxygen displacement. Inert gases such as nitrogen and argon are odorless and colorless. In the event of a leak, the oxygen in a room can drop to dangerous levels without anyone noticing. This leads to a risk of asphyxiation, especially in confined spaces where inerting systems operate continuously. This is why oxygen meters and strict access controls are indispensable in areas where inerting is used.
Static electricity
The rapid injection of gases such as carbon dioxide can create static electricity. If the atmosphere is not yet completely inert, such a spark can still cause an explosion. This risk is limited by:
• Controlled gas injection to avoid high-velocity flow.
• Proper grounding of equipment, especially when handling inerting gases in fuel tanks or sensitive materials processing.
Monitoring and backup
Because a completely guaranteed inert atmosphere is difficult to achieve, alarm systems and backups are crucial. Continuous measurement of oxygen concentration ensures that deviations are immediately noticed. These inerting systems often include automatic shutdown features if oxygen rises above safe limits, preventing unwanted combustion or explosions.
Conclusion
Inerting is an essential measure for preventing explosions and protecting sensitive products in industry. When flammable substances cannot be avoided and it is impossible to work safely outside the flammable range, inerting systems are often the only effective solution.
By lowering the oxygen concentration below the Limiting Oxygen Concentration (LOC), ignition is made impossible. At the same time, inerting prevents oxidation, moisture absorption, and unwanted combustion.
The choice of the right inert gas, the right technique (such as purging or blanketing), and compliance with ATEX guidelines are crucial in this respect. Risks such as asphyxiation and static electricity must also be managed at all times.
In short: inerting offers safety where other measures fall short but requires technical knowledge, good design, and strict control. When properly implemented, inerting processes can effectively prevent unwanted combustion and protect both people and installations against potential hazards.
