This column is about a concern, two misunderstandings, and possibly a misrepresentation.

The Concern

A cleaning solvent will catch fire. The concern is real. Halogenated solvents present a paradox to users. They contain hydrogen and carbon atomsóthe stuff of which fires are made. But they also contain halogen atomsóthe active ingredient in flame suppressants. Which one dominates? Yes, that's the question! This paradox has confused users of cleaning solvents such as HCFC 141b, 1, 1, 1 trichloroethane, methylene chloride, trichloroethylene, HFE-7200, and more recently, n-propyl bromide (n-PB).

First Misunderstanding

A solvent with no measured flash point canít catch fire. Thatís wrong; some can catch fire. All of the solvents mentioned above have no measured flash pointóyet each can be ignited. Each has a normally-measured (ASTM E- 681) value of lower and upper explosive limit (LEL and UEL). They range from 2.4 volume % to around 23 volume % in air at 25 EC respectively.

Second Misunderstanding

There are really two meanings to the term "flammability." One is technical and the other is what most users think it means.

The technical meaning is the basis for many regulations and industrial practices pertaining to cleaning solvents. Solvents are classified as flammable (flash point value < 100 EF) or combustible (100 EF > flash point value < 200 EF) based solely on this data (classification published in CFR 1910.106 (a) (18), OSHA).

The meaning commonly understood is that the described product won't burn. Definitions for "flammability" and "flammable" in various non- technical dictionaries include: "measure of the extent to which a material will support combustion," "any substance that is easily ignited, bums intensely, or has a rapid rate of flame spread," "capable of being easily ignited and of burning quickly," etc.

An Opportunity for Misrepresentation

Misrepresentation might happen if solvent suppliers used phrases in advertisements like "Flammability—None" In the case of n-PB, for example, that simple phrase points the user simultaneously in two directions. No, a flash point is not reported for n-PB by the ASTM D-56-02 or D-1310 tests. Yes, n-propyl bromide "will support combustion." Would a supplier advertise using such a phrase knowing some readers might more favorably value their product because they believe the product can't be ignited when in fact it can be ignited? I hope not!

Le Denouement

To answer the question raised above: "mechanical circumstances" dictate whether the flame suppressant atoms in a solvent molecule will overpower the tendency of hydrogen and carbon atoms to act as fuel for combustion. Said another way, the circumstances of the test dictate whether ignition is or is not achieved. These circumstances are very different for the flash point and flammability tests. See Table 1.

As you would expect, solvent molecules which have a higher ratio of flame suppressant to fuel atoms can't be ignited in either test (or in practice).

Common cleaning solvents such as HFE-7000, HFE-7100, HFE-7500, HFC 43-10 mee, HCFC 225 ca/cb, perchloroethylene, and CFC-113 fail both test approaches—no flash point or LEL or UEL values. Each solvent has a high ratio of halogen atom to fuel atoms.