I'm guessing a bit here, but the following might give you some guidelines.Doug said:Any idea of what kind of situation in your lab would result in levels above what is considered unsafe? ie one bottle open outside a fume hood for an extended period of time? a few ml of methanol evaporated over an hour? or ???
The TLV is 200 ppm (see: http://www.erowid.org/chemicals/alcohol ... heet.shtml ). The biggest variables are how much air exchange there is through the room, and the room's size.
In a normally ventilated room, I think the open bottle would definitely be above the TLV -- methanol has a pretty high vapor pressure.
As to whether a few mL evaporated over an hour would be dangerous, here is what a "worst case" calculation gives:
evaporation of 5 mL in a typical sized household room (10 x 10 x 8 foot ceiling assuming NO exchange) would give about 150 ppm methanol, below the TLV; 10 mL would give 300 ppm, above the TLV
OTOH, open two windows and run a fan to push air through the room, and these values would drop a lot. All you have to do is get a couple complete exchanges of air per hour, and the 10 mL drops well below the TLV. Hence, the reason many solvents say "use in a well-ventilated area."
You might go look up how they get TLV's on wikipedia -- the TLV is kind of a legal limit, and may or may not be a fully realistic number for decisions affecting your health. Methanol is converted to formaldhyde when metabolized (and then formic acid), both pretty toxic, but both pretty volatile themselves, so it might be that the TLV is based on some assumed (or, measured) rate of outgassing of these metabolites from the lungs. IOW, as you breathe the stuff in, some of it gets converted to the two above, and some of them gets washed out through normal breathing, so that clearing your body may be the limiting factor in picking the TLV.
IIRC, the treatment of loading you up on ethanol is designed to prevent methanol metabolism, so the methanol gets washed out as methanol, and never gets metabolized to the more toxic stuff; the "health" of your liver is another variable: if an end-stage alcoholic is exposed to the TLV, that might be a lot harder on him/her than a person with a healthy liver.
Hope this is not too much information. I feel pretty geeky getting back into this stuff! :lol: :roll: