Gas leak detection in hazardous areas

Introduction

While, in general usage, the word ‘hazard’ can refer to many different types of risks or dangers, the term ‘hazardous area’ has a very specific meaning. It is an area where explosive or flammable gases, vapours or dust may be present in sufficient quantity to create the risk of an explosion or fire. Such areas are often associated with process plants that use pressurised gases, and it is easy to see that gas leaks in those areas are likely to increase the risk level significantly. Gas leak detection plays an essential role in ensuring the safety of personnel and facilities and requires reliable and certified equipment to mitigate potential dangers. Using non-certified instruments in such environments can lead to catastrophic consequences, making selecting appropriate gas leak detection solutions essential.  

Understanding explosive atmospheres

Hazardous areas are classified into different zones based on the likelihood and duration of an explosive atmosphere. Zone 0 (gas/vapour) and Zone 20 (dust) represent areas where explosive hazards are continuously present or persist for long periods. Zone 1 (gas/vapour) and Zone 21 (dust) indicate areas where explosive atmospheres are likely to occur periodically during normal operation, while Zone 2 (gas/vapour) and Zone 22 (dust) refer to areas where explosive atmospheres are unlikely to occur or will only exist for a short time. Common explosive gases include methane, hydrogen and propane, while combustible dust can range from coal and grain to metal powders.  

Instrument safety for explosive environments

Gas leak detection instruments must be certified to meet stringent safety standards to ensure their safe operation in hazardous areas. ATEX (ATmosphères EXplosibles) certification is a requirement for equipment used within the European Union but is a recognised standard in many countries globally. ATEX-certified instruments are designed to prevent ignition sources and withstand the harsh conditions found in hazardous environments.

Intrinsic safety is a fundamental design principle for ATEX-certified equipment. It involves limiting the electrical energy available in the device to prevent sparks or thermal effects that could ignite explosive atmospheres. This is achieved through the use of barriers, voltage and current limiting components and specially designed circuits.

In addition to ATEX certification, an instrument's ingress protection (IP) rating is also important for its durability and reliability in hazardous areas. IP ratings indicate the level of protection against solid particles and liquid ingress. For example, an IP54-rated device is completely dust-protected and protected against splashing water from any direction.  

Acoustic imaging for gas leak detection

There are several options available for gas leak detection, but undoubtedly, one of the easiest, most versatile, reliable and cost-effective methods is using an acoustic imager. The operating principle of this device is simple to understand; it depends on the fact that leaks invariably generate sound. Sometimes, this is in the audible range – a hiss or a whistle – but more often, it is in the ultrasonic range and cannot be directly heard by the human ear.  

Ultrasonic imagers have an array of microphones that pick up audible and ultrasonic sounds from the leak. As would be expected, they also pick up other sounds, but signal processing suppresses the background noise to ensure the imager displays only the leak noise detail. Using a specific microphone array, along with further processing, allows the instrument to determine the direction and approximate size of the leak using a technique known as “beam-forming”.  This information is used to produce an image with the leak represented by a “cloud map” that represents the sound pressure being measured. For ease of interpretation, the “cloud map” is overlayed onto an ordinary digital image of the plant or equipment under investigation.

This method of detecting and locating faults offers several advantages, one of the most significant being that it requires no contact with the equipment or installation being examined. In fact, with Megger’s MPAC cameras, faults can be detected at distances of up to 120 m. This can be extremely important in hazardous areas, where getting close to the plant may be dangerous. The extended operating range also enables quick surveys of large installations, saving time and resources compared to traditional contact-based methods.  

Another significant advantage of acoustic imaging is its versatility in detecting leaks of any gas or vapour. Unlike some other leak detection methods that are specific to certain gases, acoustic imagers can be used to measure any pressurised gas leaks. This makes them a cost-effective solution for industries dealing with multiple types of gases or vapours.

Modern acoustic imagers, such as those in the Megger MPAC range, are designed for ease of use, even in challenging conditions. In most applications, users only need to set two parameters: frequency range and dynamic range. The best instruments have a focus function that allows them to be used even in very noisy environments as well as pinpoint and measure an individual leak. They should also estimate the leakage rate and indicate its severity and potential annual losses, all of which help the operator decide the most appropriate response to the problem.

ATEX-certified gas leak detection

Despite the many benefits of acoustic imaging for leak detection in hazardous areas, one essential point must be kept in mind: only ATEX-approved equipment can be used. It may seem unnecessary to emphasise this, especially for those who are used to working in hazardous environments, but it is important to note that many acoustic imagers do not have ATEX approval, and this may not be immediately apparent. Therefore, referring to the manufacturer’s documentation and confirming ATEX approval is always necessary before using any acoustic imager in a hazardous area application.

IP Rating for industrial applications

Care should also be taken to ensure an acoustic imager has the appropriate IP rating for the environment in which it will be used. If used within an industrial environment, an IP rating of IP54 is generally accepted as the minimum, as this will ensure the imager is protected against the ingress of dust and moisture.  

Conclusion

When selecting gas leak detection equipment for use in hazardous areas, ATEX certification is non-negotiable. It is essential to verify that the instrument has the necessary approvals to ensure compliance and safety. Additionally, considering the device's IP rating is important to ensure reliable operation in the harsh conditions often encountered in industrial environments.

Acoustic imaging has proven to be a valuable tool for gas leak detection in hazardous areas, offering unique advantages over traditional methods. Its ability to detect leaks from a safe distance, precise localisation capabilities and versatility in detecting various gases make it an efficient and effective solution. The escape of gases – which may be potentially explosive, poisonous, harmful to the environment, very costly, or even all of these things – can be minimised.  

Find out more about Megger’s MPAC128-ATEX acoustic imager and how it can effectively mitigate risks, ensure compliance and create safer working environments.