HAZMAT Sensors - Page 1
Forum section: electronics / general

author: bullet308
author_rank: Frequent Contributor
timestamp: June 11, 2012, 02:33:33 am
content: Hi:I was wondering if anybody here knew much about systems for detecting various hazardous gases and integration of same with microprocessors? I note that there are inexpensive sensors available that cover things like volatile organics, CO2 and ammonia. Chlorine seems to be more problematic, or at least fewer sensors seem to be available. I gather that multiple sensors would be required to cover a fairly wide range of toxic gases, and there might be some issues with shelf life and durability of the sensors as well.This strikes me as a reasonable extension of my interest in the detection and metrology of ionizing radiation. Other reasons are to be found in the articles linked below, both of which incidents took place near where my family and I live and work:http://en.wikipedia.org/wiki/Graniteville_train_disasterhttp://www.thestate.com/2009/07/16/865114/ammonia-cloud-kills-woman-injures.htmlAny insight would be appreciated.

author: IanB
author_rank: Super Contributor
timestamp: June 11, 2012, 02:56:57 am
content: I don't know much about the technical details, but I don't think the electronics are the main issue. It's all going to be about the sensors themselves.Most sensors are designed to be installed where a given hazard is reasonably expected. For instance in a chemical plant where chlorine gas is processed or used you will expect to find chlorine gas detectors placed in relevant locations. Those detectors might perhaps be mislead by other substances, but if those other substances are not present in the plant it doesn't matter.It doesn't even matter if a sensor might not discriminate against two dangerous substances, since the action in both cases is going to be to evacuate to a safe distance. You evacuate first to put personnel at a safe distance, then you figure out exactly what is going on.There's not much you can do about releases in public areas according to the news articles you linked. On the one hand a train crash could happen anywhere and is unpredictable. Your nose is going to be the most sensitive detector around when it comes to chlorine or ammonia or other pungent gases. If you smell it, get away from there.If the release happens in a chemical or industrial plant that you live near to, then make sure you know the emergency protocols beforehand. Know what the siren sounds like, know when it isn't a drill, and know what the evacuation routes are.

author: Barryg41
author_rank: Contributor
timestamp: June 11, 2012, 03:15:28 am
content: I have to agree with IanB.I work at a plant that uses Ethylene gas as our feed stock. But we have propylene, butene, hexene, vinyl acetate and hexane just for starters. We only have one sensor for all of those gases. We and HAZMAT rely on OUR detectors and nothing else. They are calibrated once a 12 hour shift with a known trace. Parts are changed out pretty often.VOC and IDLH ppm's are most important on evacuation, but LEL and UEL determines when and where we move the locals or barricades.Tell me, how close would you be to a BLEVE situation? How would you know it's a BLEVE situation?Listening to the emergency personel that is helping you evacuate is the most important thing you do in a emergency.

author: FenderBender
author_rank: Super Contributor
timestamp: June 11, 2012, 03:53:34 am
content: Well it's probably not going to help you, but here's something that might be of interest, for whatever reason.

author: free_electron
author_rank: Super Contributor
timestamp: June 11, 2012, 04:40:42 am
content: the sensor we use in the cleanroom is actually a gas chromatograph ... we got some really nasty stuff. silicontetrachloride , silane , hydrogen fluoride , arsine , fosfine , borane ...sampling heads continuously suck air into a combustion chamber where it is burned. theemitted light is sent through a prism and alinearccd looks for spikes in the spectrum.if the red lights start blinking . get out of there .... it means arsine or fosfine has been detected. and that stuff will kill you.

author: bullet308
author_rank: Frequent Contributor
timestamp: June 11, 2012, 02:08:43 pm
content: Thanks for the feedback, all. I was already gathering that this was a relatively complex field, and now realize that it is worse than I thought. :-/There are solid-state sensors for some things that I think are fairly low maintenance, such as these items:http://www.ebay.com/dsc/i.html?LH_TitleDesc=1&_sacat=0&_nkw=arduino+gas+sensor&_osacat=0&_odkw=arduino+gas+sensorHowever, they are only suited to a limited number of hazardous gasses and I am not sure how suited they are for life safety applications. Lots of organics, ammonia, smoke, steam...simple. Glad that ammonia is one of them. As toxic agents go, chlorine seems to be one of the bigger challenges. From what I gather, all of those sensors are "wet" chemistry and short-lived.The video above does a great job of outlining the issues, including the need for pricey semi-disposable sensors that need very frequent calibration. Problematic. :-/ It was also a nice little primer on intrinsically safe design. Now I know why the intrinsically safe version of Ludlum's flagship survey meter is twice as expensive as a normal Model 3.http://www.ludlums.com/component/virtuemart/?page=shop.product_details&flypage=flypage_ludlum.tpl&product_id=137&category_id=17&activetab=introWith it being able to drive scintillation probes up to 1,200 volts, I imagine that is quite a challenge.As stated above, the electronics are essentially pretty simple, but then if I want to engineer them to meet an intrinsically safe standard, that is a whole other matter again.BLEVE and spills in general are a potential issue for me personally, as I live within a mile of a major railroad mainline and propane gas pipeline (that are co-located!) and two miles of two interstate highways and a major propane gas terminal. The concept is something that you can mount in or around your house or in a vehicle to give you a heads-up in the event you blunder into something or something crawls through you HVAC system at night.I have no problems listening to authorities as to when to bugout, as I used to kinda' be one of those authorities (ex-state Emergency Management), but sometimes you get the word right after you stop breathing, which is a little late. :-/Thanks for all your help.