What is Intrinsically Safe?

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⌚Timestamps:
00:00 - Intro
01:10 - Risk assessment
01:48 - Intrinsically safe levels
02:44 - How to apply standards
02:51 - Barriers
03:56 - Examples
05:48 - Decreasing the dust

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In this video, we will explain what it means to be intrinsically safe. We will explain why being intrinsically safe is important to an automation professional.

We will also explain where intrinsic safety should be considered. Then we will provide a few examples of how to design intrinsically safe circuits.

Intrinsic safety has to do with preventing fires that could occur because of sparks or heat sources.
Being intrinsically safe in an electrical sense means restricting the current flow or preventing sparks in a hazardous environment.

An intrinsically unsafe environment could cause a fire or even an explosion by something as simple as a wire being cut. We need to be aware of the environment we are working in, especially when working in potentially hazardous environments.

If you are working in or around hazardous environments, it is imperative that a risk assessment is done to help identify the risks. Knowing the risks in any environment will help you mitigate those risks and keep you and others safe.

There are two main types of classifications:
– ATEX,
– NEC (NFPA70).

We will focus on the UL (Underwriters’ Laboratories) standard for intrinsic safety.
There are three main types of NEC 70 intrinsically safe levels: Class I, Class II, and Class III.

– The Class I environment has to do with flammable gasses and vapors. These vapors could be gasoline, hydrogen, natural gas propane, ethanol, or methane. These gasses exist under normal operating conditions and abnormal operating conditions.

– The Class II environment has to do with combustible dusts. Some possible dusts include metal and metal alloys, charcoal, carbon black, flour, plastics, grains, and wood. These dusts exist under normal operating conditions and abnormal operating conditions.

– Class III has to do with flying objects or fibers.

In intrinsically safe environments it is necessary to use special circuits to help protect from explosions and fires. Electrically speaking we do this by using optic isolation or by current-limiting devices. The industry term is a barrier.

Barriers come in many shapes and sizes but they all optically isolate the sensor in the environment from the electrical cabinet.

An optic isolator is a set of electrical components that connect two circuits optically. The components of an optic isolator are a diode and a light-sensitive transistor usually packaged in a chip.

Because of optic isolation different voltages can be used, which helps in an environment that needs intrinsic safety devices.

In some situations, there will need to be more done with the electrical panel than just installing barriers.

The panels in the room with the flour conveyor will need to be pressurized with some sort of compressed gas. This is usually compressed air, which causes positive pressure on the panel and decreases the likelihood of the flour dust getting in the panel.

Because of the compressed air, each panel will need to be sealed with some sort of putty or sealant.

To follow the Class II, DIV 2 standard pressure switches will need to be installed.
When a panel is opened, the switches will turn on a red strobe light, alerting those working nearby that the room is unsafe.

When designing a Class II, DIV 1 panel there are more restrictions. DIV 1 refers to the presence of a hazardous atmosphere under abnormal operating conditions.

Just like the Class II, DIV 2 environment, a Class II, DIV 1 will need pressure switches for loss of pressure and they will additionally need to remove line power to every panel in the room when the pressure is not safe.

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