Posted By Philip Beale
"hand held vision aids"

A bit vague what exactly are you looking for?

Phil

Posted By Julian Meer (at Work)
Fred,

For IS apparatus there are ignition curves of voltage v current against each of the gas groups (I, IA, IB, IC). The ones I have seen are logarithmic with an origin y=10 mA, x = 10V (don’t switch off as these values may help you a lot). IS being one principle of Ex protection.

My challenge was could I allow an experienced chemical plant fitter to wear a blood pressure monitoring device with his normal hard days work within the zoned areas of our plant. Now, IS designers or validaters may scream at this (in which case I would welcome their constructive feedback) but, by working with the technicians at the hospital, I was able to show that even a short circuit within the monitoring device was at an mamp-volt (= mJ energy) below the ignition energy of that gas / vapour.

I then considered if a fault condition within the device was able to exceed the autoignition energy of our dangerous substances (as defined by DSEAR). Given the AT was 496 deg C I didn’t considered this likely else such devices would be an alternative energy supply.

My conclusion was that this device was safe given stipulations 1, 2, 3 and 4 below. I have been to refineries were I have had to hand in my watch and car fob, equally I have been to others were this hasn’t been required. I have been plants with zoned areas were only Ex mobiles are allowed, and equivalent plants in the US were non-Ex mobiles were allowed (nor Factory Mutual equivalents). In otherwords, there are some types of non-Ex portable electrical equipment which on risk assessment could be shown to be suitable or not.

Perhaps if you asked the manufacturers for the equivalent data. Bodies like Sira and Hexagon Technology are very good at offering cost-effective advice in such situations

Stipulations were: 1) no removal of battery; 2) exit hazardous if device is known to have become damaged; 3) no work in a confined space or line breaking; 4) exit any area if vapours seem more than normal (odours may be less than 5 ppm, but LEL are usually 10,000 ppm plus). Another layer of the protection was that the plant is covered by an extensive network of gas detectors which alarm at 10% LEL and or operated hard wire trips shutting off possible offending flows.

Ex hearing aids are quite common in the process industries though so maybe you search will be successful. The DSEAR ACOPS and BS60079 series should also be able to help your risk assessment if you choose that path.

I won’t comment on making labels bigger or if anyone with such poor eyesight is medically fit enough to work alone within the demands of areas where explosive atmospheres may occur, especially within an emergency. Whoops sorry I have! One can’t afford to misread something in a hazardous area, e.g., motor ident, instrument number, less they introduce a hazard to themselves or colleagues. Seriously, it may be for your risk assessment and good luck. Sincerely hope this helps.