Gas sensors are a crucial part of many industries. Employees and employers aliksensor e rely on these instruments to keep them safe. And while it may be tempting to think that these sensors are all the same, they are not. Some are more accurate than others. And some are safer than others. In terms of safety, an explosion-proof sensor enclosure is an important component of sensor design.
The reality is that when you use a gas sensor, you are potentially putting electrical equipment in the vicinity of hazardous gases. These gases only need a spark to cause a fire – or worse – an explosion. Without an explosion-proof sensor enclosure, you could have a recipe for disaster.
Intrinsically Safe vs. Explosion-Proof Sensor Enclosures
There are two different categories that you may see when looking at sensors. It is important to understand the difference between them. They are:
- Intrinsically Safe (IS): An intrinsically safe designation describes sensors designed and fabricated to operate using low amounts of power. In fact, the voltage is low enough that it cannot ignite flammable material. These sensors limit the energy available so that they can operate in hazardous areas.
- Explosion Proof (XP): Explosion-proof describes a sensor that is housed in explosion-proof enclosures. The housing around the sensor is strong enough to contain a fire or an explosion. This design is preferable in settings where it is impossible to reduce the necessary electrical circuit energy.
How do Explosion-Proof Sensor Enclosures Work?
Explosion-proof sensors allow for an explosion inside the electrical instrument, so they do not prevent ignition. However, the design and construction of the housing prevent the explosion from escaping the instrument. Therefore, while there is an internal explosion, it will not spread to the explosive atmosphere. These explosion-proof enclosures can incorporate several different design elements to achieve their goal. For example, they can achieve an appropriate thickness in the case wall, comply with gap dimensions, and incorporate additional specifications for installation.
These sensor enclosures do not prevent an explosion but prevent them from spreading to the atmosphere. The International Electrotechnical Commission (IEC) has developed a Zone system, which the United States recognizes. This system classifies hazardous locations based on the level of risk. The breakdown is as follows:
- Zone 0: Areas where flammable gas is continuously present or present for long periods (typically over 1000 hours/year).
- Zone 1: Areas where flammable gas may exist under normal operating conditions (typically 10-1000 hours/year).
- Zone 2: Areas where flammable gas is not likely to occur. If it does, it is unlikely to be present for a long period. Typically, this standard would be defined as 10 hours or less per year.
The Zone system also adds a temperature class/code. This code indicates the maximum surface temperature of the housing.
The classification of sensor apparatuses follows the Zone system. However, there are additional industry certifications that can provide more information. These include:
- ATEX: ATEX certification is based on a European Union directive covering “equipment and protective systems intended for use in potentially explosive atmospheres.” All equipment and protective systems intended for use in the EU must be ATEX certified. The certification would be similar to the standards set by OSHA or NEC in the US.
- IECEx: IECEx is an international system for certification of equipment for use in an explosive atmosphere. Its quality assessment specifications are based on standards prepared by the International Electrotechnical Commission. The goal of this standard is to establish a required level of safety while making international commerce easier. When multiple countries agree on a standard, it’s easier to understand what it entails. IECEx also aimed to:
- Reduce manufacturers’ testing and certification costs.
- Reduce time to market.
- Foster international confidence in the product assessment process and the equipment and services covered by IECEx Certification.
- Provide one international database listing.
- FM: FM stands for Factory Mutual. They are an organization that provides standards, testing, and certification in the United States. They are similar to UL, or Underwriters Laboratories, who do the same function in the US. The Canadian Standard Organization serves this function in Canada. Unlike IECEx, these certifications are only valid within the country they are issued unless they are part of a program allowing certification to be recognized across borders (UL, FM, and CSA all have valid certifications in both countries).
Design Features & Benefits of Explosion-Proof Sensor Enclosures
Explosion-proof sensor enclosures offer a multitude of design options for reliable explosion protection in any setting. A critical design feature in explosion-proof enclosures is the flame path. These paths enable burnt gases from the internal explosion to cool down. After cooling, they exit the enclosure so that they can no longer ignite the potentially explosive atmosphere outside. The design of the flame path is critical in ensuring the safety of the enclosure and sensor operation.
Another important factor is the thickness of the enclosure walls. These walls have to be designed carefully to regulate heat transfer from within the enclosure. In the event of an internal explosion, it is essential that the temperature of the outer surface of the housing does not rise too high. If it passes a certain threshold temperature, the surrounding fuel-air mixture can be ignited.
The proper selection, installation, and maintenance of sensors will prevent explosions in most circumstances. However, it’s important to recognize that classification systems can be confusing. But it is vital that operators understand the difference between different zones, certifications, and types of enclosures. Acceptable protection methods can only be identified if everyone understands the risks and can make informed choices.
Explosion-proof sensor enclosures play a vital function in protecting workers and property from hazardous conditions. These enclosures must be strong enough to contain the internal explosion. And this means you must select them from a brand you can trust. Even one failure could lead to the loss of life. To learn more about explosion-proof sensor enclosures, contact the team at NevadaNano today.