CRIB

/ CHM 605 Quiz 7
Oct 9, 2008

NOTE ON extinguisher exercise: There will be (at least) two lines, every person is to experience discharging a CO2 extinguisher and dry powder extinguishers. Make sure that after you’ve done one, you get in another line and do the other. There MIGHT be a demonstration with diesel fuel (which is somewhat impressive depending on how much fuel they use and how much the wind blows).

FINISH THE QUIZ BEFORE getting off the bus for the fire extinguisher exercise. Confer as you prefer.

Given these data and symbols:

NFPA 704 symbol / Other info
/ acetonitrile
b.p. 82 oC, fl.pt. 2 oC, PEL 40
/ methanol
b.p. 65 oC, fl.pt. 11 oC, PEL 200
/ acetone
b.p. 56 oC, fl.pt. -18 oC, PEL 1000
/ tetrahydrofuran
b.p. 66 oC, fl.pt. -21 oC, PEL 200
/ methylene chloride
b.p. 40 oC, fl.pt. -none, PEL 12.5

NFPA = National Fire Protection Association and the 704 diamond was devised to convey FIRE SITUATION HAZARDS TO FIREFIGHTERS.

  1. Say something about the relative toxicities (in “fire situations”) of the five different substances.

methylene chloride, THF, and acetonitrile are regarded as a higher hazard for human health

2. Why would methylene chloride have a 1 (one) in the flammability section? (Halogenated solvents are generally regarded as non-flammable.)

At elevated temperatures, CH2Cl2 becomes a fire hazard. It has no published flash point (see definition above), but at temperatures above 100 C it does have explosivity limits. LEL = 12 %, UEL = 23 %. (I’m guessing that the flash point test returns “none” because the composition 1 cm from the liquid’s surface is always too rich to ignite, i.e. always > 23%.)

3. Which are regarded as the more poisonous substances according to their PELs and how well does this info agree with the numbers in the blue boxes? Any outstanding oddity? (compare acetone and MeOH.)

acetone and methanol are both a “1” for human health in the NFPA diamond, but the PEL of methanol is much lower (200 ppm, as contrasted with 1000 for acetone), suggesting that methanol is in fact more toxic. The difference is that PEL are for inhalation of the vapor, not exposure to the combustion products, which is what the NFPA diamond represents.

4. Any suggestion/idea why THF has the 1 (one) in the reactivity section? (But all the others are zero?)

Dry THF (and some other common others like Et2O and p-dioxane) form peroxides if stored for longer than 6 mo or a year. These pose an additional explosion hazard.