Intrinsic Safe Barriers in Hazardous Area Package

Instrumentation
1

Question:

Have a query regarding Intrinsic Safe IS/NIS barriers. Working on Hazardous area package (Palletizer) for Zone 22. Photocells / Photoelectric sensors are certified as Ex ‘t’.

Also the Enclosures that the sensors are to be connected are Ex ‘t’ certified. Do I require barriers to be installed for the same?

If yes why?

And if not then why not?

Exactly how do we define the requirement for barriers.?

Answer:

The use of barriers in hazardous areas, such as Zone 22 (an area where a combustible dust atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only), is often associated with protecting intrinsically safe (IS) circuits. Intrinsic safety is a protection method employed in potentially explosive atmospheres, and barriers are used to limit the energy available to the electrical equipment in the hazardous area.

In the case of your Palletizer, with photoelectric sensors and enclosures certified as Ex ‘t’ (protection by enclosure), here’s the analysis:

If Barriers are Required:

  • Yes: If the sensors and enclosures are part of an intrinsically safe system, and the equipment is certified for intrinsic safety (Ex ‘i’), barriers might be necessary. They would be used to limit the energy (voltage and current) to a safe level that cannot ignite the hazardous atmosphere.

If Barriers are Not Required:

  • No: If the sensors and enclosures are certified as Ex ‘t’, they are designed to contain an internal explosion or prevent the ignition of an external explosive atmosphere. This type of protection does not inherently require energy limitation through barriers, as it relies on the containment method.

Conclusion:

Based on the information provided, since the devices are certified as Ex ‘t’, it would generally indicate that barriers are not required. However, the final determination must be based on a full analysis of the system, including:

  1. Standards and Regulations: Local and international standards, such as IEC 60079, may have specific requirements.
  2. Equipment Certification: Detailed examination of the specific certification and its conditions for safe use.
  3. System Design: Understanding the entire system and how the devices are connected can impact the need for barriers.
  4. Risk Assessment: Consultation with a hazardous area specialist or conducting a Hazardous Area Classification (HAC) study to ensure that all aspects are covered, including the interaction between different devices and the overall safety philosophy.