What is a flame arrestor in an Ex zone? A key element of explosion protection!

A flame arrestor is one of the most important elements in protecting an installation against the spread of an explosion. It protects pipelines, tanks and ventilation systems against the effects of gas or vapour ignition. In this article, you will learn how it works, what types there are and in which situations it is mandatory.

What does a flame arrestor do and why is it mandatory in Ex zones?

A flame arrestor is a device that stops the spread of fire and explosions in gas and steam installations without blocking the flow of media under normal operating conditions. It protects against the ingress of flames into the installation, which in practice means preventing a catastrophic scenario.

In practice:

• acts as a barrier between the danger zone and the interior of the installation,
• allows gas to pass through, but blocks fire and high temperatures,
• protects tanks, pipelines and other components from the effects of ignition.

Importantly, circuit breakers are not an accessory – in many cases, they are required by regulations, including EN ISO 16852 and the ATEX directive. The lack of such protection may mean that the installation simply should not operate in an Ex zone.

Not all interrupters work the same way – see how they differ.

There are several types of interrupters available on the market, but they cannot be used interchangeably.

You will most often encounter:

• end-of-line – installed at the outlet, e.g. from the tank vent,
  
• in-line – between installation components to stop the flame in the pipe,
  
• to deflagration – for “slower” explosions (below the speed of sound),
  
• to detonation – where pressure and velocity are much higher.
  

What works in one installation may be completely unsuitable in another. The wrong choice can invalidate approvals and even compromise safety. That is why it is so important to know the differences and not cut corners.

When the explosion accelerates – and how a breaker can stop it

Not every explosion looks the same. Sometimes we deal with what is known as deflagration – that is, combustion at a speed slower than sound. But if conditions are favourable (e.g. a long, narrow pipe, a lot of turbulence), detonation can occur, i.e. a violent shock wave that cannot be stopped so easily.

What can increase this risk:

• pipeline length and diameter (the higher the L/D ratio, the worse),
  
• presence of bends, narrowings, valves,
  
• high initial temperature and pressure.
  

A detonation breaker must be much stronger than a standard one. It withstands much higher pressure, has a different internal design and often requires more space for installation.  If you are unsure what kind of explosion may occur in your system, it is not worth guessing. It is better to choose a model that will protect you even in the most unpredictable scenario.

Where are flame arresters installed? Not only in large plants.

Flame arresters are not reserved exclusively for refineries or large chemical plants. They are used wherever combustible gases, vapours or mixtures thereof may occur in a system.  Even in smaller installations – such as biogas stations, container reactors, sewage tanks or cisterns.

Examples of installation locations:

• ventilation systems for tanks containing flammable liquids,
  
• waste gas combustion installations,
  
• recirculation lines in chemical processes,
  
• reactor degassing or breathing systems.

Many failures and explosions were caused by the lack of a circuit breaker where it should have been. Therefore, it is worth checking your installations – even if they are small but work with flammable media.

Service and operational errors – what are the most common problems?

The most common problem is not the selection itself, but the fact that no one checks the breaker afterwards. And yet it is an element that comes into contact with gases, dust and moisture – and wears out over time.

What to watch out for:

• contaminants blocking internal channels,
  
• mechanical damage and corrosion,
  
• no control of flow resistance and pressure.
  

The standards clearly state: interrupters must be checked regularly, cleaned, and their clearance and tightness inspected. Otherwise, they may not work when they are really needed.

More and more models now have the ability to monitor parameters in real time, e.g. via pressure or temperature sensors. This is an option worth considering, especially where access to the device is difficult or working conditions are demanding.

Are you planning to invest in a flame arrestor? Let us assist you!

Choosing the right flame arrestor is not just a matter of compliance with regulations. It is a real decision that can stop an explosion before it causes damage. If you are unsure which model is right for your installation, we can advise you.
We can help with:

• selection of circuit breakers compliant with ATEX and EN ISO 16852,
  
• explosion risk assessment and gas flow analysis,
  
• matching breakers to venting, combustion and recirculation systems,
  
• documentation for acceptance by the Technical Inspection Authority or Ex audit.
  

Do not leave it until the last minute – in installations with flammable gases or vapours, a minor technical difference can make a big difference.

Frequently asked questions about flame arresters

Does every system with combustible gases need to have a flame arrestor?

Not all of them, but many do. The obligation depends on whether there is a risk of flame reversal – e.g. through ventilation, venting or gas recirculation.

What is the difference between a deflagration interrupter and a detonation interrupter?

Deflagration stops “slow” explosions, while detonation stops much stronger, fast shock waves. Their design, resistance and method of installation are completely different.

How often do flame interrupters need to be serviced?

Regular inspection is recommended – the frequency depends on the working conditions. Gas deposits or corrosion are enough to cause the breaker to malfunction.

Does the breaker work in both directions of flow?

Not always. Most models operate in one direction – the one in which we expect ignition to occur. Bidirectional models are available, but they must be chosen carefully.

Can the circuit breaker be installed independently, or must it be connected to other safety devices?

It can operate independently, but in many cases it is part of a larger explosion protection system – e.g. with non-return valves, HRD systems or earthing.