Q&A about intrinsically safe measurement devices

Automotive paint booth
Juhani Lehto
Product Manager for high-end products
Published: Jan 27, 2021
Industrial Manufacturing and Processes
Industrial Measurements

In this Q&A blog we take a look at what we mean when we talk about intrinsically safe devices, where they can be installed, and what other safety precautions need to be considered when using them. We also briefly discuss the benefits of using these types of devices in hazardous areas.

Q: What does intrinsically safe mean?
A: Intrinsically safe, or Ex i, describes a device that works on such a low current and voltage that it cannot possibly ignite flammable material. This type of device cannot cause a hazardous event because the energy it needs is below the level needed for ignition. Intrinsic safety is a globally recognized protection concept.

Q: Can I install an intrinsically safe device directly in a hazardous environment or do I need to take some other precautions as well?
A: An intrinsically safe device is not completely safe unless it is installed in combination with a device that forms a barrier between the hazardous zone and an unclassified (safe) area. For example, power and signal wiring that crosses into the hazardous zone must be secured with an intrinsically safe galvanically isolated barrier or Zener diode barrier located in the safe area. This barrier prevents dangerously high currents or voltages from being transmitted to hazardous areas where they could cause electrical failure of the intrinsically safe device and form a source of ignition.

Q: Why do I need safety barriers if the device itself is considered safe?
A: The design of Ex i devices only takes into account the functioning of the device itself in specific foreseeable failure situations. The device is designed so that ignition energy levels are not exceeded as long as the characteristic voltage, current, capacitance, and inductance values are not exceeded. The device is, of course, part of an electrical circuit. This means that the safety of the entire circuit – including the devices located in the safe area – must be considered, as dangerously high amounts of electrical energy could accumulate due to a failure elsewhere in the circuit. For this reason, the Ex i device must be separated from the rest of the circuit by a barrier located in the safe area. 

Q: How do I recognize an intrinsically safe product?
A: The Ex-mark on a product always includes the type of protection offered. The “i” in Ex i indicates that a product is intrinsically safe. Typically, the mark also includes another letter indicating the severity of the hazardous area it is suitable for. For example, the Vaisala Humidity and Temperature Transmitter HMT360 has the “ia” marking, meaning it can be used in environments where flammable gas or dust mixtures are continuously present (zone 0/20). Alternatively, “ib” would indicate zone 1/21, where explosive hazards may occur only periodically and for a short duration; “ic” indicates the least hazardous zone, 2/22, where explosive hazards may occur only during abnormal conditions.

Q: What are the benefits of using an intrinsically safe product?
A: Intrinsically safe devices provide explosion protection through ‘natural’ means as they are intrinsically incapable of storing enough energy to create a spark. This means that they do not need heavy flameproof enclosures, continuous overpressure purging with compressed air, or other cumbersome alternatives that exist to enable inherently unsafe designs to be used in areas with explosion hazards. As a result, they are usually no bigger or complex than general purpose non-Ex devices.  

Learn more about our intrinsically safe humidity and temperature transmitter series or contact us for more information.

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