Explosion protection and temperature sensing

Explosive atmospheres are a significant risk to people and property in a variety of industries such as petro-chemical, food processing, recycling and mining

In order to maintain a high level of safety and explosion protection, global regulations, standards and legislation have been developed through the International Electrical Committee (IEC) . For the European Union, these IEC Explosion (Ex) regulations have been compiled into the ATEX Directive.

What are hazardous zones?

A potentially explosive atmosphere (also called a hazardous zone) exists where combustible gasses, dust, mist and vapors are at risk of forming an explosion due to the combined presence of oxygen and an ignition source. Ignition sources could be any of a large number of triggers such as:

• open flames
• air/oxygen
• hot surfaces
• electrical or mechanical sparks
• electrical, atmospheric or electro-static discharge
• ultrasound
• chemical reaction
• optical radiation (visible light, ultraviolet light or infrared light)

In order to protect installations from a potential explosion it is important to analyze and classify different hazardous zones. As such, the most appropriate equipment can be selected to ultimately prevent or contain an explosion. A hazardous zone is defined by three criteria:

1. What type of hazard is it?
   Gas, vapor, dust or fiber grouped according to ATEX zones.
2. What is the auto ignition temperature of the hazardous material?
   Also called temperature or T-rating this refers to how easily a hazardous material can be ignited, with hydrogen being the most at risk to ignition. Equipment that is used in a hazardous zone must be given a T-rating to ensure it will not contribute any potential ignition triggers (such as a surface above a certain temperature).
3. What is the likelihood of the hazardous material being present in risky (flammable) concentrations?
   Particular zones (0,1 and 2) are specified in ATEX to indicate how long hazardous material is present. The longer it is present the greater the explosive risk.

ATEX certified or ATEX ready

ATEX (explosion protection) certification is a process that ensures that equipment and protective systems designed for use in potentially explosive atmospheres meet the required regulations, standards and directives. Manufacturers in the European Union, have to certify that their products will not cause an explosion during routine operation in potentially explosive atmospheres. It covers essential health and safety measures for:

• Primary explosion protection by preventing the creation of an explosive atmosphere/hazardous area.
• Secondary explosion protection by preventing the ignition of an explosive atmosphere

Note that ATEX standards may also apply to safety, controlling or regulating devices that are required to avoid explosions, even if these devices are placed outside of the potentially explosive atmosphere. It is for this reason that we at Kamet have ensured we can supply various ATEX certified or ATEX ready components and sensors (e.g. cable, sensors, connection heads and instrument housings).

What are the ATEX zones?

The ATEX directive recognises two types of ATEX atmospheres:

• Explosive gas, vapor and mist environments (ATEX zones 0, 1 and 2)
  • air mixed with flammable substances
  • ATEX marking ‘GB’
  • subdivided according to minimum ignition current and the amount of time they are present during normal operation.
• Explosive dust atmospheres (ATEX zones 20, 21 and 22)
  • air mixed with flammable substances in the form of dust or fibers
  • ATEX marking ‘Db’
  • Subdivided according to the type of dust and relative flammability

The following table summarizes the zones. :

*It is always possible to use a higher rated Protection Type than necessary for a particular Zone.

Explosion protection measures

In order to ensure the potential for an explosion is removed or significantly reduced, a variety of approaches can be used. These include:

• Intrinsic safety:
  • Preventing a potential ignition arising
  • Limiting the ignition energy of the equipment
• Explosion proofing:
  • Preventing the explosive atmosphere contacting the ignition source
  • Prevent an ignition trigger from escaping outside the equipment
• Pressurization or purging:
  • The potentially explosive atmosphere is entirely isolated from the electrical equipment by filling the equipments enclosure with an inert gas

ATEX codes indicate the type of protection method for which equipment has been certified. This code consists of an Ex (explosion) followed by a letter. Here is a brief overview of some of the most common letters:

• Ex d is commonly known as explosion proof, but that is inaccurate, it is actually flameproof, meaning it can contain a flame and prevent it from escaping to the hazardous atmosphere.
• Ex q prevents transmission of explosion outside (explosion proof)
• Ex e indicatesincreased safety due to the lack of arcs, sparks or hot surfaces
• Ex m refers to an encapsulation which prevents the hazardous atmosphere from reaching any potentially flammable parts.
• Ex n means non-sparking and it is limited to Zone 2 environments.
• Ex ia is intrinsically safe and suitable for Zone 0 or 20, the most high risk ATEX zones.
• Ex p keeps the flammable substance away from the electrical equipment (using purging or pressurization)

Sensors for explosive atmosphere

Explosion protection is a vast subject matter, well beyond the scope of this article. We include it here in our knowledge base because Kamet’s temperature sensing components have an important role to play in measuring and transmitting accurate temperature readings in potentially explosive environments. They are used both in the application’s equipment and atmosphere to make sure maximum and minimum temperatures are not being exceeded at any point.

At Kamet we can help you with choosing the correct components to ensure your process is ATEX compliant. The Kamet team is happy to answer any questions you might have in this regard. You can contact us here.

More about selecting temperature sensors for potentially explosive (Ex) atmospheres.