Last week we defined hazardous locations, and discussed the basics of both protection methods and hazardous area classifications. This week, I want to discuss intrinsic safety, what it is, and how it prevents igniting a disaster.
James Wilkinson, Automation Specialist at R. Stahl, defines intrinsic safety as the following:
Intrinsic safety can be defined as an explosion protection technique that is applied to electrical equipment and wiring to limit both electrical and thermal energy under both normal and abnormal conditions to levels that are insufficient to ignite the hazardous mixture that is present in the hazardous area.
CSA International provides a definition as well:
Intrinsic safety involves limiting the electrical energy at potential sources of ignition in electrical circuits (hot components and spark sources) to such low levels that – even under abnormal (fault) conditions – there is no possibility of the electrical energy igniting an explosive atmosphere. This method of protection may be used for a wide range of low power equipment, including pagers, process control tank level transmitters, and portable gas detectors.
Simply put, intrinsic safety is designing an electrical instrument so that it requires very little power to operate. So little power, in fact, that it cannot ignite a hazardous mixture. Sensors are certified intrinsically safe (IS) by agencies such as CSA International.
Keeping the power low enough to avoid ignition is a matter of good sensor design, and proper wiring. Purchasing a sensor that is certified intrinsically safe simply isn’t enough. Without good wiring, power can still fluctuate.
In addition to intrinsically safe instrumentation, an intrinsically safe barrier or isolator is also required. These devices control how much power can pass through to the sensor, and are wired between the sensor and the control system or power source.
We are often asked about simple devices. A simple device is a sensor that does not store or generate more than 1.5V, 0.1A, 25mW, or 20?J, such as one of our float switches. These sensors do not need an intrinsically safe certification, due to their low power operation. However, they still need a barrier or an isolator to regulate the power source when installed in a hazardous area.
Intrinsic safety is a great protection method for hazardous locations. It effectively prevents fire and explosions by never supplying enough spark or heat to make it happen. Let us know if you have any questions about intrinsic safety, simple devices, or intrinsically safe wiring.