Alright,this may seem like a whole new level of dumb,but I would like to know how to detect various toxic gasses. Some of the gasses that I am
planning to work with in the near future include:
I would like a reliable way to detect them when they are approaching potentially dangerous concentrations.
[Edited on 24-2-2016 by SmellNoEvil]ave369 - 24-2-2016 at 12:31
Chlorine, hydrogen chloride and bromide, ammonia and formaldehyde can be detected by smell before they get dangerous. Chlorine smells like bleach,
ammonia like... well, ammonia, and formaldehyde has a stinging odor. The acid gases smell like the corresponding acids.
Hydrogen sulfide is the trickiest and the most dangerous of all listed gases. At first, it is detectable by odor, but then the nose stops detecting
it. If you catch the tiniest whiff of rotten eggs while working with sulfides, open all windows IMMEDIATELY and stop the reaction if you can.MrHomeScientist - 24-2-2016 at 13:13
Each one has specific circumstances for detection, so you'd need to set up something unique for each. I recall you posted earlier about lacking a
sense of smell, which ave369 may have missed (it wouldn't hurt to stress that point again). So barring smelling anything, there are tests for various
gases you can do. Just off the top of my head:
Chlorine and bromine will bleach pH paper. Hang a few strips around your workspace, or periodically wave one over your reaction apparatus to detect
leaks.
Ammonia gas reacts with HCl vapors to form a dense white smoke of harmless ammonium chloride, so an open watch glass of muriatic acid should serve as
a good visual indicator. Or again, wave an open bottle of hydrochloric acid near your apparatus and watch for smoke. Do the inverse if you're working
with HCl instead. (HBr may perform similarly, but that's just conjecture)
Hydrogen sulfide test strips are commonly available, or you can make some yourself with by soaking a strip of filter paper in lead acetate solution. I
believe they need to be damp to work properly. Same as for chlorine, just hang several strips around your work area. They turn black in the presence
of H<sub>2</sub>S IIRC.
But just googling for "[x] gas detection" I'm sure many answers will present themselves.mayko - 24-2-2016 at 13:19
Chlorine and bromine are oxidizers; their presence can be detected by potassium iodide and starch; a piece of paper dipped in the mixture and kept
moist, or a beaker stirring the solution, should be able to detect them.
Ammonia and haloacids vapors react to create white ammonium halide suspension; a bit of cotton soaked in one will appear to smoke in the presence of
the other.
Many of those compounds irritate the eyes in high concentrations.DJF90 - 24-2-2016 at 15:32
I would like a reliable way to detect them when they are approaching potentially dangerous concentrations.
I know this may not be what you want to hear, but perhaps you should avoid such toxic gases with compromised olefactory response, or at least work
alongside someone who can detect their presence. That tends to be the standard practice for working with cyanides, in my experience anyway.
Thats not to say you cannot enjoy chemistry as a hobby, you just have to be a little more selective about what you can do independently.
Odour tends to be a very sensitive detection method (typically ppm), far more so than many of the qualitative tests provided above.
Be safe.BromicAcid - 24-2-2016 at 18:48
Above are some good chemical detection systems. But if you're serious about working with a highly poisonous gas like hydrogen sulfide, you should
invest in proper safety equipment. I single out hydrogen sulfide because it can 'deactivate' gas mask filters, olfactory fatigue can set in, and it
is downright toxic. By proper safety equipment I mean a personal detection monitor. These are electronic systems that are calibrated for a single or
multiple gasses, they give readouts in PPM or PPB depending on their make, and they can cost from $10-200 if you keep an eye out on eBay. At least
consider it, it may be worth the investment. The proper search term would be the gases name followed by "personal monitor" not in quotes. One issue
I have run into in the past though is that these monitors do not have batteries that are easily replaced. The last one I bought had a dead battery, I
pulled it apart and it was a lithium/thionyl chloride battery. Not easy to find a replacement for.JJay - 24-2-2016 at 19:13
Miners used to keep birds in mines to detect poisonous gases. That might be considered inhumane these days, but if you don't have a specific poison
gas detector, it's better than dying.Deathunter88 - 24-2-2016 at 19:21
Miners used to keep birds in mines to detect poisonous gases. That might be considered inhumane these days, but if you don't have a specific poison
gas detector, it's better than dying.
I disagree, you should not be keeping a bird with the sole purpose of seeing it die just to save yourself. And most of the time when the miners used
the birds, they didn't die, only fainted. On a side note birds are EXTREMELY sensitive to gases. The bird of a friend of mine died because he was
heating copper sulfate. The trace amounts of sulfuric acid that vaporized was enough to kill the bird. Many bird keepers find that the birds in their
house die when they use PTFE cookware due to the minute amount of toxic gas that is produced.
1. Don't use another living animal as "sacrifice" just so you can pursue a hobby.
2. This would be extremely ineffective since the birds would die when you perform pretty much any experiment. j_sum1 - 24-2-2016 at 21:25
Avian physiology is all about the lungs. Extreme gas transfer efficiency is required to support energy intensive actions like flying. Thus birds are
extremely susceptible to toxic compounds in the air.
But, agreed, for a large number of reasons, a lab canary is not really the kind of gas detector you need.
My thoughts...
And in writing this, I am attempting to answer some issues in SmellNoEvil's other thread
The way I see it, SmellNoEvil's predicament is really not that different to anyone else's. Smell does not really correlate well with toxicity anyway.
So he misses out on some of the interesting sensory part of chemistry -- smelling esters and the like. (We have a whole thread on the smell of
solvents. Chloroform wins as I recall.) In terms of safety, you shouldn't really be relying too much on smell to save you anyway. I see a few
different chemical scenarios.
(1) There is plenty of non-volatile chemistry that can be done -- solution chemistry, crystal growing, radiochemistry, analytical work and so on.
(2) There is the kind of chemistry that is done out of doors and with good ventilation anyway. Thermites, EM, and so on. Sure, gases are produced
but smelling them is not really part of the experience.
(3) There is the truly toxic kind of chemistry -- HF, HCN, phosgene etc. Smell is not even a consideration in this scenario. Whether you have a
sense of smell or not, you don't want any kind of contact with these things. If SmellNoEvil wants to get into that field then he needs to take
exactly the same precautions as the rest of us.
(4) That leaves kind of the middle ground -- the kinds of gases that are not extremely toxic but should be avoided. Ideally you are not relying on
your sense of smell to save you. These include solvent vapours, Cl2, Br2, CO, SO2 and NO2. H2S is probably either on this list or #3. Here is my
advice -- which correlates with what IrC and others have said.
You want a fume hood or good extraction system.
Invest in some smoke bombs and set them off periodically so that you can see where your gases are going and check that you are protected.
Research your experiments beforehand so that you know what gases are possible in any given experiment.
If there are risks, put detectors in place to give you warning.
CO detectors are cheap enough to buy.
Wet strips of filter paper with copper sulfate or lead acetate solution will give you warning of H2S
Wet strips of indicator will let you know if acidic or basic fumes are floating around.
Starch indicator paper will go black in the presence of Cl2, Br2
NO2 is generally visible and usually expected. There is probably a good indicator strip that you can make for that too.
HCN -- not sure what the best detector would be. Worth looking up. Or avoiding altogether.
I feel like I missed something. I hope this helps.
[edit]
Yep missed something. H2S is probably either in category 3 or 4 – not 1 or 4 as I said before.
As an aside:
I tend to be a bit blase about H2S myself. I lived in an area renown for geothermal activity and really got used to the smell. It doesn't bother me
and actually brings back good memories. I am aware of the desensitising effect that it has and realise that if I wait until I find it unpleasant,
that is likely a higher concentration than others would tolerate. So I evacuate early. And I do not rely on ventilation / extraction and consequent
lack of smell to tell me I am safe.
[Edited on 25-2-2016 by j_sum1]Herr Haber - 25-2-2016 at 03:06
Just adding a point to j_sum1 said just above:
Most of the gasses cited in point 4 will also have an effect on throat and lungs (Cl2, Br2, So2 etc.) and in minute quantities you should still get
the warning sign you'd get even with a sense of smell without being in too much of a danger.
Just saying this out of my head: I dont know your conditions at all but I can certainly imagine it poses quite a few challenges if you're interested
in chemistry.
All the DIY detectors above are good ideas. I'd avoid HCN myself anyway unless outside, with a strong Wind and a gas mask if I were you.
There are also the more permanent solutions like Equipment From Draeger. Some is cheap, some will be unaffordable but you can still look for their
Equipment on eBay and hope for a bargain. Their CO and H2S detectors are not "that" expensive I'm told.SmellNoEvil - 25-2-2016 at 10:15
Most of my concerns have been covered, except detecting nitrogen dioxide, sulfur dioxide, and formaldehyde.
This is speculation,but I think that NO2 can be detected using PH paper, is that true?
A quick look through EBay results on sulfur dioxide detectors showed equipment that costs at least $74, that's not something I am enthusiastic about
spending money on. Is there any DIY method of detecting SO2?DJF90 - 25-2-2016 at 11:58
Nitrogen dioxide is also detected by starch iodide paper according to the equation:
2KI + 2NO2 => 2KNO2 + I2
NO2 and SO2 are also acidic gases, so they'll give a reaction with moist pH or litmus paper.
Draeger tubes have already been mentioned... IIRC their brochure gives a chemical explanation for the detection method which may allow you to
determine what the contained reagents are. I suspect indicator strips can be fashioned using the same or similar reagents.
[Edited on 25-2-2016 by DJF90]MrHomeScientist - 25-2-2016 at 13:11
Ask yourself this, though: Is your life worth $74?
Potentially life-saving PPE is something everyone should be enthusiastic about investing in.BromicAcid - 25-2-2016 at 13:59
NO2 and SO2 are also acidic gases, so they'll give a reaction with moist pH or litmus paper.
In theory, but when I have tried to use pH paper to test for SO<sub>2</sub> in the past the sulfur dioxide bleached the pH paper and
rendered it useless.
