Solvents

Safe Handling of Solvents depends on:

1. understanding the hazards, and
2. being careful and prepared.

The flammability and/or toxicity of solvents are commonly the most talked about hazards. But many solvents are also extremely irritating to the skin and mucous membranes. One consideration which is of particular concern to chemists is pressure buildup (due to exothermicity of rxn in a volatile solvent) in reaction vessels with limited gas outlet capability.

The information table below provides information on the properties of a number of common solvents as regards their boiling, igniting, expoding, poisoning....

Limits for storage of flammable materials in buildings and in rooms are established by State Fire Codes. The definitions of classes of flammable and combustible liquids, and the limitations for storage, are provided by the REM web site on the Flammable and Combustible Liquids webpage.

Info table for some common organic liquids

The flash point of a material is defined as the temperature at which an ignition source 1 cm from the surface of the liquid will cause ignition. The standard method is defined by ASTM and most flash points are measured in a "closed cup" flashpoint tester. Discrepancies/disagreements are found in the literature for some substances, but the values are usually fairly close.

Dichloromethane has upper and lower explosion limits! While generally regarded as nonflammable, and although no flashpoint can be measured by the standard method, dichloromethane (methylene chloride) has known explosive limits in air mixtures at 100°C and above, and is known by firefighters to give flammable/explosive mixtures with air if there is a high energy ignition source or an enriched oxygen content.

Explosive limits - flammable solvents are an explosion hazard when the solvent vapor concentration in air is greater than the lower explosive limit (LEL) and less than the upper explosive limit (UEL). Below the LEL, the mixture is too lean to burn. For example, the LEL of ethyl alcohol is 3.3%. Note that this is 33,000 ppm for comparison with the permissible exposure level of 1000 ppm.

PEL - The OSHA Permissible Exposure Limit is a regulatory limit for the concentration of a contaminant in workplace air. The values shown refer to the level as an 8h-TWA (8 hour time weighted average) unless otherwise noted, given in ppm (parts per million in contaminated air) unless otherwise noted. See OSHA Z-1 and Z-2 tables.

Ethanol/water solutions: The flash point increases as ethanol is diluted with water, but not real fast. Flash point of 80% ethanol/water is about 24°C, and for 70% EtOH/water it's 29°C (according to Aldrich catalogue).

Flammability class: IA, IB, IC, II, IIIA, and IIIB classes are defined by NFPA (National Fire Protection Association) depending on flash points and boiling points. See REM web page chart for more info

Chloroform's PEL is not an 8 hour time-weighted average but a CEILING which is not to be exceeded even momentrily.

Note on ppm - to get a feeling for the ppm concept at a tangible level, consider the volume of a recognizable room or two, and what ppm concentration of solvent would be created by evaporating ONE MOLE of solvent into that room, assuming STP, ideal gas behavior, and uniform dispersion of the vapor.

WTHR 127A
solvent room
12' x 14' x 12'

2016 ft3 = 57,087 L

WTHR 560
old lab in attic
24' x 42' x 12'

12096 ft3 = 342,521 L

Evaporate a mole of solvent at STP and you get about 22.4 L if it's an ideal gas, right?

WTHR 127A: i.e., 392 ppm

WTHR 560: i.e. 65.4 ppm

Note: ppms are like percentages but you multiple by 106 instead of by 100

Therefore, a mole of CH2Cl2 (85 g, or about 65 mL), would create a concentration of 427 ppm in WTHR 127A, or a concentration of 71.2 ppm in WTHR 560 (if Temp is ZERO Celcius). So would a mole of acetone (58 g, or about 72 mL)

Odor threshold - Given in ppm, taken from one or more available references. There are only a few things you can surmise about exposure using odor thresholds. For example, Chloroform has OT of 192 ppm and PEL of 2 ppm. This means that if you can smell it, you're way over. It does NOT mean that if you can't smell it you're not being overexposed. On the other hand, acetone odor becomes obvious to the average nose at 2 ppm, far below the PEL of 1000 ppm, so not smelling it is an indication that you're not being overexposed (if you have that average nose). Odor threshold sources are shown here:

• 2-Propanol: http://chem-courses.ucsd.edu/CoursePages/Uglabs/MSDS/2-propanol.-fisher.html (1996) and https://nj.gov/health/eoh/rtkweb/documents/fs/1076.pdf
• Ethanol: http://chem-courses.ucsd.edu/CoursePages/Uglabs/MSDS/ethanol.propanol.methanol.-baker.html (1996)
• Acetone: http://chem-courses.ucsd.edu/CoursePages/Uglabs/MSDS/acetone.-baxter.html (1996)
• Chloroform: https://www.mcs.com/~meridian/chlorina.html
• Methylene chloride: https://nj.gov/health/eoh/rtkweb/documents/fs/1255.pdf
• p-Dioxane: https://nj.gov/health/eoh/rtkweb/documents/fs/0789.pdf
• Acetonitrile: https://nj.gov/health/eoh/rtkweb/documents/fs/0008.pdf
• Toluene: https://nj.gov/health/eoh/rtkweb/documents/fs/1866.pdf
• Xylenes: https://nj.gov/health/eoh/rtkweb/documents/fs/2014.pdf
• Benzene: https://nj.gov/health/eoh/rtkweb/documents/fs/0197.pdf and https://chem-courses.ucsd.edu/CoursePages/Uglabs/MSDS/benzene.-fisher.html
• Ether: https://www.qrc.com/hhmi/science/labsafe/lcsstxt/lcsstx30.htm

Methylene Chloride got its own OSHA Standard and a drastically lowered PEL in 1997. The Standard is at 29 CFR 1910.1052. As with all the other Subpart Z standards (29 CFR 1910.1000 through 1910.1201), the only parts that apply to laboratory use of chemicals are the PEL, any prohibition of eye and skin contact, and if the action level (or in the absence of an action level, the PEL) for the material is routinely exceeded, then exposure monitoring and medical surveillance are required. It is also "reasonably anticipated to be a human carcinogen" by NTP 8th report, and "possibly carcinogenic to humans" according to the IARC evaluation.

Benzene also has its own special section in OSHA subpart Z, and is "known to be a human carcinogen" as per NTP 8th Report. and listed as "carcinogenic to humans" by the IARC evaluations

Chloroform is "possibly carcinogen to humans" in the IARC evaluation, and "reasonably anticipated to be a human carcinogen" by NTP 8th Report.

1,4-Dioxane (p-dioxane) is "reasonably antipated to be a human carcinogen" by the NTP 8th Report, and Possibly carcingoenic to humans" by IARC Evaluation.