Is fiber ok in hazardous environments*?
We got this question in one of our PROFINET one-day training classes while explaining APL (Advanced Physical Layer). Ethernet is not intrinsically safe. Since IEEE 100BASE-TX Ethernet is the base technology for PROFINET, PROFINET cannot reach hazardous environments.
There are options to go around this limitation. Some factories employ containment methods such as strong enough cabinets to hold the explosion’s energy. Also, some specialized vendors have developed fiber optics (FO) cables/connectors for hazardous areas. But in general, FO cables can introduce an ignition source in a hazardous environment. They are not intrinsically safe. Fiber optics cables may not have that high voltage/current in copper wires, but light beams inside the cables can turn into an ignition source in four ways:
1. Optical radiation can be absorbed by surfaces which are heated by light and reach the ignition temperature of the surrounding atmosphere.
2. If the wavelength of the optic radiation matches the absorption band of the explosive gas then thermal ignition can occur. Ammonia, Butane, Propane, and Heptane are some examples of explosive gases.
3. Light emissions come in many different wavelengths from infrared to UV. These waves can react with oxygen molecules in the area to generate an ‘oxidant’ that could ignite.
4. If a ‘laser beam’ of optical radiation hits a potentially explosive gas it can generate plasma or a shock wave – both of these are ignition sources
Until intrinsically safe Ethernet is available, there is always the option to use a proxy in your PROFINET network to reach those hazardous environments without risk.
*A hazardous area is any space in which you can expect a flammable/explosive atmosphere. It requires special precautions for operation. There are three factors which have to be present in order for there to have a fire or an explosion. The three factors are fuel, oxygen, and heat (or ignition source).