Estimating Hydrogen Sulfide Exposure..

[upbeforedawn2018]

https://chemistry.stackexchange.com/posts/136639/timeline

I unknowingly exposed myself to hydrogen sulfide gas and am trying to figure out how much Hydrogen Sulfide gas i may have been exposed to.

I mixed .5 grams of Sodium Sulfide Nonahydrate into a solution containing excess acid (NH4+) as shown below.

KH2PO4  0.4 grams
NA2HPO4 0.53  grams
NH4CL   4.0 grams
Na2S.9H2O   0.5  grams

100mL water

If all the Na2S.9H2O reacts as i expect , then 70.83mg of Hydrogen Sulfide are produced.

At room temperature and one atmosphere (inside of a small room say a studio sized room), is there any way to estimate how much exposure I received? in terms of PPM given how much Hydrogen Sulfide was produced?

I immediately smelled rotten eggs and then the smell went away after a second. Is this because I inhaled so much? Or because it dissipated so quickly?

That Hydrogen Sulfide is heavy also complicates things (does it not spread as easily? would it settle around me instead of spreading all around the room?)

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To add, this paper shows that most of the hydrogen sulfide is released from solution amost immediately in HEPES buffer, so I wonder if it would be the same here, and what that means for exposure (did i just breath in most of the hydrogen sulfide at once,  or did it spread out  into the air so fast i did not breath much in?)

https://www.sciencedirect.com/science/article/pii/S0003269711006695?via%3Dihub

"A preweighed crystal was dropped into an open 150-ml beaker containing 100 ml of
Hepes buffer (arrow). The solution was mixed with a magnetic stir bar, and H2S
was recorded with the H2S sensor. More than 80% of the H2S was formed during the
first 10 s, essentially as fast as the crystals was dissolved, and H2S
concentration subsequently declined due to volatilization. Panels A and B are
from the same experiment with different time scales."

[scooke]

Dear John,

While hydrogen sulfide is a noxious and toxic gas, its odor threshold (ppb) is much lower than its toxity levels.  The amount of continuous exposure that one can experience without adverse effect is well below the amount that was released by your experiment.  Even high exposures are completely recoverable as long as they did not result in severe injury or death.  That is why a "time-weighted average" (TWA) is used as long as the exposure is below immediately toxic levels.

https://www.airgas.com/msds/001029.pdf 

Your immediate exposure could not be more than the entire amount (70.83mg = 0.0023mole = 0.052L = 0.00184ft3) dispersed in the volume up to your nose.  Approximating a 27ft3 (3-ft cube) immediate volume results in a concentration of about 6.8ppm, so easily under the STEL of 15ppm for a possible maximum short-term exposure as the dispersion may not be linear.

H2S does eventually dull the smell perception, but that usually takes quite some time working in TWA-allowed concentrations for several minutes or longer.

Work safely!

Steven

[mbdowell]

John, if we assume that hydrogen sulfide mixed well with the air in the room and that you left the room within 15 minutes, then at least you haven't exceeded OSHA exposure limits. If (or, after) the gas is well mixed, 70 mg is 2 millimole and the volume at STP is ~45 mL. A 10 ft x 10 ft room with furniture might have 25 M3 = 25,000 L of air, so your volume concentration is ~2 ppm Airgas's MSDS was at hand and it says that the OSHA limit is 15 ppm for 15 minutes.But if you had ingested 

Of course the gas wasn't mixed well at the start. You got a much more concentrated whiff and it put your nose out of commission for a while, as hydrogen sulfide does. But if you had ingested all 70 mg, that would be only ~ 1 ppm body weight. I'm not up to date on acute toxicology but Peter Cooper's "Poisoning by Drugs and Chemicals" (2nd ed., 1958) says that if you've been exposed to less than 200 ppm and have survived four hours, the headaches will go away and you'll be all right. 

Hoping that you are OK!

Mike Dowell 

[scooke]

Dear Michael,

I've worked my entire career in the gas industry, with extensive use of H2S.  For individual exposure I prefer to err on the side of caution.  Actual exposure is usually much higher than an "after-the-fact" equilibration to a full room (or other) volume.  While this incident was in no way dangerous, the conditions or materials could have easily been different.  I recommend trying to calculate exposure levels as closely to the actual person-contact as possible.  I have been involved in one recovery and one post-mortem due to hydrogen sulfide exposure, so I can't stress proper procedure, PPE, and planning enough.

Best regards,

Steven

[mbdowell]

Steven, you make the excellent point that although gas exposure for a few minutes in a well-mixed room would be considered below OSHA toxicity levels, John had a direct acute exposure close up and he's asked about that as well. You have direct experience here. But you also are asking "can John tell us what caused this unanticipated result?" John, you've shown us some good observations and you're in a forum where many are interested in developing better lab procedures. What strikes you, and what might you do differently next time?  

[upbeforedawn2018]

Steven,

Thank you so so much. I was incredibly concerned because when I tried to do the calculations of 70.83mg/m^3  to get PPM i was getting ~50ppm and the distance from me to the opening in the beaker was definitely less than 1 meter. Is PPM calculated by dividing .00184ft^3 / 27 ft^3  and multiplying that by 10^6 (one million?), because that yields 68? (Hopefully not!)  6.8 is much better of a level.

I am sure about the amounts of reactant i used. Is it possible because i was  standing directly above the beaker I was exposed to more? I ask because I recently developed muscle twitching that started around the same time. I went to see a physician and they said it should go away and it is possible the twitching is unrelated (due to medication i was taking). 

At the very least this has been a crash course in chemistry again for me and reminded me how interwoven chemistry and biology inevitably are! 

I will definitely be more careful about my reactants and always use a chemical hood from now on. Steven Cooke‌

[scooke]

Dear John,

Yes, AND always check and double-check your values and calculations!  You added a couple of orders of magnitude to the volume of H2S released from my calculations.  Be cautious, but don't make it worse than it is either.

You do bring up a key point that those of us in practice often assume - ALL noxious compounds (and especially toxic ones) should ONLY be handled in a good fume hood!!

Best regards,

Steven

[scooke]

Dear Michael,

Those are some good additional points or topics, but don't put the words in my mouth.  Or, did you mean to phrase it as a rhetorical question?  There is always a broad interface across encouraging individual experimentation with assumed (incorrectly) safeguards and simply telling people that only "professionals" should do those things, and a formal course with supervision should be taken before undertaking such home activities.

We do hope that discussion boards such as this one are used (and supported by ACS chemists!) to help "regular" people to enjoy the wonder and utility of chemistry safely.

Best regards,

Steven

[upbeforedawn2018]

Dear Steven, Steven Cooke‌
I will absolutely remember that about noxious compounds. That's such a good point. 

I apologize for one more question about clarification. I put the wrong number in my response but when calculating PPM...

(70.83mg = 0.0023mole = 0.052L = 0.00184ft3) dispersed in the 27ft3 immediate volume. 

.00184ft3 H2S / 27ft3 = 0.000068  = 6.8 e-5 

6.8e-5 x 10^6 = 68 PPM

Is that correct? I apologize for asking further clarification. I am having some trouble finding the calculation for PPM by volume/volume online and the number (68ppm vs 6.8 ppm)worries me. 

____________________________________________________

One more chemistry question! H2S  and other gases is very small, on the order of 0.0003 to .006 microns. A surgical mask would likely make no difference in exposure/absorption would it? I am guessing protection would need to be on the order of a special filter or something that absorbs or reacts with the H2S to make it harmless. It seems a chemical hood is the best protection after all.