Tony,
Good comments.
You mention the card reader and keypad are low voltage devices. The voltage, by itself, doesn't allow devices to skirt the Intrinsic Safe (IS) regulations.
I participated in several IS product designs. Products had to withstand
two simultaneous failures without causing a spark or release of energy. For testing safety in a dusty environment, the circuit boards were coated in flour, then faults were deliberately caused. (failed component, shorts, etc) . If the flour even got scorched, that's a failure. For vapor environments, they tested with a fume-filled chamber. ANY spark could ignite the vapors.
Even a 5V problem can cause a spark. For IS products, you couldn't let the user plug in a 5V battery charger (to recharge a handheld product for instance), because that could/would cause a spark. The products had to prevent connecting the charger, say with a cover that switched off the product if the charging connector was exposed. To re-charge the product, the user was required to leave the IS classified environment. Even though the
charger was
not IS, and should
never be brought into an IS environment, we had to prevent any chuckle-head user from doing something stupid like bringing the charger into that IS workspace and cause a spark.
Spark-causing failures included foreign objects entering the product. Metal dust, shavings, paper clip could cause a spark. Typically, we eliminated any ingress points. We'd conformal coat PCBs to minimize the chance that dust (or condensation) could cause a spark. Nevertheless, the UL folks tested the products w/o conformal coating. Logic: conformal coating isn't perfect, can develop cracks (say from dropping the product), and it only tries to
contain a problem instead of eliminating the cause of spark (through safe design).
Capacitors, ie: energy storage devices, were difficult to design-in. The total capacitance of the product was severely limited.
Fuses weren't allowed. When they blow, that's an "ignition" - dangerous, even for sealed fuses.
The Underwriters Lab was extremely involved, and participated in schematic reviews, PCB layout reviews, and would question just about all design decisions. They had veto powers.
IS was very expensive - for development. Hence, IS products are expensive, to recoup the investment (for the low-volume IS market)
"Non-Incendive" (NI) rating had a lower bar. And so the products were much more affordable.
Our safety/regulatory engineers often helped customers determine if an IS product was
required for the customer's application. Or if an NI product could be used. I asked our Safety Engineer about gas dispensers ("gas pumps") at fuel stations (including ones with electric displays built in). His answer touched on several considerations:
- Gasoline fumes sink. So ground level could require an IS device, a little higher might only require an NI device. And higher still, neither certification was required. Note: This might explain the AC outlet you mentioned, which was mounted up high.
- A gas station is not an enclosed environment, so the concentration of fumes was limited.
- He agreed the new style pumps (back then) with displays, keypads, card readers likely didn't have an IS rating. Maybe an NI rating, but likely not.
- a Gas Station is not an inherently "Hazardous Environment". When compared to environments that required IS devices, like chemical manufacturing plants, mines, some engine rooms, ordinance storage, etc.
Story: We made a handheld computer that contained a bar code scanner. The military wanted to use it to scan ordinance in bunkers. We determined that within one foot, the environment required IS products. So we took our NI product and put a 1ft rod on the front. Like a cat whisker like old folks put on their car, to help stay away from the curb. So the soldiers, when scanning bar codes on the "bombs", wouldn't get too close to the triggers.
Yes, the small CRT on gas pumps was many years ago. Back when LCD displays didn't work well outdoors or in well lit environments. Other display technologies (plasma, LED, ELD) weren't mainstream). So I date myself!
Long answer - hopefully you find it interesting....
Fastb