Thanks, however the information does not cover it.

I have been a Professional Engineer for 35 years, but when I was doing the P&ID's, it was the first time I ever heard of this.

Essentially, an intrinsically safe device is one that can be safely operated in an explosive atmosphere. On this job there were Intrinsically Safe Barriers and Intrinsically Safe Multiplexers. As an example, the control for a motor drive would be passed from the PLC to the motor with an intrinsically safe barrier device located in the control room. The barrier was there to prevent/isolate the potential ignition source from the potentially explosive atmosphere. An intrinsically safe multiplexer is a device that can pass multiple controls.

In the days of dialup modems, they were required to be fitted with opto-couplers to make sure that if something went horribly wrong with the modem, the low voltage telephone system was isolated from the high voltage power supply system.

Many intrinsically safe devices come with a "schematic" of the device on a label. The only problem was that each device from a different manufacturer used different symbols to indicate this.

The best "compromise" I could come up was to use a rectangle of about 3:1 proportions with a double diagonal line through it. The controls connect to the short sides. For an intrinsically safe multiplexer, one of the formed triangles was filled in.

So far, all those installing the equipment have been able to understand this, however my client and I are trying to find some standardised backing for what we have used as this may end up being used elsewhere around the globe.

I don't want to believe that a P&ID element could be devised without an appropriate symbol.

My reason for posting this here was that these devices have ATEX certification.

Thanks. ■