Is a safety barrier required?
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I have a question: since some parts of the site require explosion protection and flameproof instruments are used there, is it then unnecessary to use safety barriers on the DCS side?
Field intrinsically safe instruments; no safety barrier is required on the control room side. Because flameproof instruments are usually not intrinsically safe instruments. Explosion-proof instruments must meet explosion-proof requirements, including the instrument itself needing to comply with these standards, as well as the installation and maintenance of such instruments having to adhere to explosion-proof specifications. The laying of signal cables and the entrances for instrument cables must meet explosion-proof requirements (such as gland fittings, sealing tubes, and sealant used for sealing).
A safety barrier is required because there are explosion-proof requirements in the site; the safety barrier functions to limit current and voltage as well as to isolate energy.
In normal facilities, instruments with the appropriate explosion-proof rating can be selected. Whether a distributor or isolator is added on the control system side depends on whether such a requirement exists. It can be omitted if not required. If the site is in Zone 1 and intrinsically safe instruments are chosen for use there, then an intrinsically safe circuit is typically formed by combining the intrinsically safe instruments at the site, intrinsically safe cables, and a safety barrier. In this case, a safety barrier must be added.
On-site explosion-proof instruments do not require a safety barrier
Intrinsic safety types must be used; flameproof types are not necessary!
I. According to current standards, explosive gas environments are classified into Zones 0, 1, 2, and Additional Zone 2. II. When it is Zone 1, Zone 2, or Additional Zone 2, flameproof instruments or intrinsically safe instruments are usually used. III. Flameproof instruments do not need to pass through a safety barrier, nor should they do so. In addition, there are dual-certification explosion-proof instruments, namely flameproof + intrinsically safe types; when used in an intrinsically safe circuit, an instrument, wiring, and a safety barrier are required to form such a circuit.
Explosion protection is like a young man, with a strong exterior. Ben is like a young girl, with a power-limiting design for the circuit. The two use different technologies respectively and are not related to each other. The key is: which technology do you want to use? One will suffice.
Explosion-proof instruments do not require a safety barrier, but it is recommended to add one; the purpose is to isolate the field area and prevent damage to the DCS cards in case wires are disconnected there. Although flameproof instruments require power to be turned off before the cover can be opened, I’ve never seen that factory perform maintenance on flameproof instruments by turning off the power first; so... don’t rely too much on such practices. Using a barrier is the proper approach. For low-power flameproof instruments, a safety barrier can also work. Since most flameproof instruments have relatively high power consumption, using a safety lock generally isn’t effective; therefore, it’s recommended to use a barrier instead……