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Let's Examine the Facts
There has been much discussion concerning the relative worker health and safety of methylene chloride strippers and their replacements. The following table contains data from the MSDS’S provided by the manufacturers of the various solvents present in methylene chloride strippers and the various replacement strippers.
| Compound | Vapor Pressure @ 68 F*. MM |
Relative Evaporation Rate** |
OSHA TLV*** (PPM) |
|---|---|---|---|
| Methylene Chloride | 355 | 7.0 | 25 |
| Methanol | 96 | 2.0 | 200 |
| Toluene | 22 | 2.0 | 100 |
| M-Pyrol | <0.32 | <0.1 | 100 |
| Dibasic Esters | 0.2 | <0.1 | 1.5 (Dupont) |
| Ethyl 3-Ethoxypropionate | 0.7 | 0.12 | 50 |
| D-Limonene | 2.0 | <0.5 | Non Established |
| Acetone | 157 | 5.6 | 750 |
| Methyl Ethyl Ketone | 75 | 6.0 | 200 |
| Xylene | 6.0 | 0.8 | 100 |
| * Pressure exerted by a vapor. For
example, the freeboard in a closed dip tank containing methylene
chloride will contain 47% methylene chloride vapors by volume (470,000
PPM). By contrast a dip tank containing M-Pyrol would have a freeboard
concentration of 0.04% (400 PPM). ** Butyl Acetate equals 1 *** A time weighted 8-hour average |
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Since the workers performing stripping operations will (if they have any sense) be wearing protective gloves and aprons etc. to prevent skin contact, the primary source of worker exposure is by inhalation of vapors produced as a result of evaporation.
M-Pyrol is a solvent which is the primary ingredient in many of the methylene chloride replacements being formulated. Various parties have written letters to Professional Refinishing magazine questioning the safety of M-Pyrol. They have cited such things as embryo toxicity in rats and mice at very high levels and a TLV of 100.
A simple calculation using the data in the above table can be used to determine the relative inhalation hazard of the different replacement solvents compared to methylene chloride.
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Completing the calculation for M-Pyrol ((7.0/0.1)*(100/25)=280) reveals that the inhalation hazard is 280 times less than that of methylene chloride under identical ventilation conditions. Even dibasic esters with a Dupont recommended TLV of 1.5 PPM has an inhalation hazard over 4 times less than that of methylene chloride as a result of its very low evaporation rate.
The foregoing is not intended to imply that you can ignore potential hazards when using methylene chloride replacements or that methylene chloride cannot be used safely. The calculation simply points out that safe working conditions are much easier and less expensive to implement when using the replacement strippers.
R.G. Esposito PhD.
Seneca Research Inc.
Keuka Business Park
Penn Yan, NY 14527
315-536-0269
E-Mail senecaresearch@verizon.net