How to calculate ppm generated of formaldehyde in batch

[ahumza94]

Have a batch with a 3 lb curative package. The curative package contains .1 weight percent formaldehyde. Its a butyl rubber based batch mixed in a banbury mixer so a lot of heat is generated from the rubber masticating. The batch mixes until it reaches 350F and then we dump the batch.
Question: We are trying to calculate how much formaldehyde is generated in ppm during the batch to see if our respirators can handle it and to also get an LEL %. Now the picture attached is our industrial hygienist way of calculating ppm. She calculated that we were generating a concentration of formaldehyde by taking the mass of formaldehyde in the batch (solid/liquid mass) of .3 lbs and dividing it by a rough estimate of the volume of the mixer. This is incorrect right? We need to take into account the vapor pressure of formaldehyde at the elevated batch temperatures using clausius clapeyron eq or antoine's parameters right ??? Am I missing something here? Please look at picture and I can provide more info as well.
Thanks!

 

[IRstuff]

She correctly did a worst-case analysis, which is where all of the formaldehyde does into vapor into the worst-case smallest volume.

However, you say, and her calculation uses, 0.1% by weight (1/1000), so that should be 0.003 lb, unless I'm missing something here. That drops the worst-case to 15.384 ppm.

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[ahumza94]

Ok,
I just slapped myself, can't believe I missed that. I guess I was thinking since liquid-->gas has volume expansion, but there's still mass conservation law that applies between vapor and liquid. Also I was skeptical at the 15000+ ppm calculated because I was there during the a batch and I am not dead so yeah. We actually measured our ppm using draeger tube and it came out to around 9-10 ppm. So as you said this is worst case.

Thanks for not calling me an idiot lol.

Humza A

 

[IRstuff]

No worries; the only scary thing is that your measurement is not too far from a worst-case that should never happen. Hope that you take appropriate precautions.

TTFN (ta ta for now)
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