Halogenated Solvent Exposure – How low will it go?

Throughout the United States, many manufacturers may need to change the cleaning agents and/or cleaning equipment used for critical product cleaning. One reason is that the allowable worker exposure to key chlorinated and brominated solvents may become far lower. The reduced levels will come not from OSHA but rather as a result of U.S. EPA “amended TSCA” activities. This includes determination by EPA of unreasonable risks to workers for four solvents. The concept of unreasonable risk is a bit difficult to address. It isn’t quantitative. We now have some indication of the numbers (the acceptable or allowable or maybe reasonable exposure numbers). Here are some very, very preliminary, unofficial maximum allowable 8 hour exposure levels that EPA might propose.

n-propyl bromide (nPB, 1-bromopropane) 0.05 ppm
perchloroethylene (PCE, perc) 0.2 ppm
trichloroethylene (TCE) 0.001 ppm
methylene chloride (MC, dichloromethane) 1 ppm (potential ban on vapor degreasing)

Exposure numbers have been decreasing, but the potential proposed EPA numbers are much, much lower than most safety professionals and cleaning equipment designers are accustomed to. For example, for TCE, the Cal/OSHA PEL is 25 ppm; the ACGIH TLV© 8-hour TWA is 10 ppm. There may be a ban on MC in vapor degreasing because EPA will probably also add a very low short term exposure number (STEL).

The end of open top vapor degreasing?
If anything like the proposed EPA worker exposure numbers were to be adopted, it would mean the end of open-top degreasing for these “classic” halogenated solvents. Open-top degreasers are those where there is an air/solvent interface. An open-top degreaser with a closable lid or with really “tight” controls or multiple chilling coils above the solvent, is still an-open top system. As a practical matter, it is likely to be impossible to obtain adequate solvent containment in open-top vapor degreasers. Safety professionals tend to informally adopt an “action level” of half the 8 hour employee exposure.

Airless/airtight/vacuum
We have seen indications that, as a practical matter, 8 hour levels for perchloroethylene can be achieved in “airless/vacuum” cleaning systems, where, as we explained, by design and by operating process, there is no air/solvent interface. Manufacturers of such systems have worked to achieve containment below what is currently required. However, what we currently understand could be the proposed levels are orders of magnitude lower than what even airless/vacuum have tried to measure – suppliers have aimed to stay far lower than current requirements. Be aware that there is a substantial capital investment for such systems.

Unreasonable risk -> reasonable
We think the entire manufacturing community will find it useful to have exposure numbers, in part because EPA documents indicate a determination (or what might be termed an assertion) of unreasonable risk to workers for the four solvents. What’s unreasonable? Given that there are risks to everything, how can we move from unreasonable to reasonable? Manufacturers of vapor degreasers and of airless/vacuum cleaning systems could determine worker exposure relative to existing requirements; it is impossible to relate achieved worker exposure to “unreasonable risk.”

Manufacturers of cleaning equipment may find the lower numbers to be distressing, but they provide a goal (albeit a challenging goal). This would allow the process of data gathering, recommended process design, and perhaps for equipment design.

Safety professionals might consider the technical aspects of measuring employee exposure and also consider the potential of engineering controls (including personal protective equipment). 

What about HFE/HFO blends?
trans-1,2-dichloroethylene, (trans-DCE), a major component of effective “designer solvent” blends, is currently under review by the EPA; and some submitted toxicity data is available on the EPA website. Azeotropic solvent blends containing trans-DCE can be used in some newer open-top degreasers. They could also be used in airless systems. Blends that are not true azeotropes pose fire hazards. Further, technical performance of these blends depends on the process, including the soil and substrate. The process would have to be reevaluated. If trans-DCE were to be heavily regulated, there would be a seismic shift in the way products are cleaning and in the way suppliers are monitored or audited by final product assemblers.

Plan, don’t panic
This is an important time for awareness These numbers are preliminary. It is based on the best information we have currently; and the numbers may change. We do not know the scope of actions that the EPA could propose and what the consequences might be. We will keep you appraised of developments.

Suppliers of halogenated solvents are already making business decisions, including a decision by one supplier to cease U.S. production of TCE. As a result, there are already TCE shortages. 

It is an important time to understand your options and to become educated about the pros and cons of various cleaning processes relative to YOUR application, to YOUR, workers, to YOUR customer base. It is time for you to become the critical cleaning expert. On a technical and performance level, the loss of options for effective cleaning is problematic.

Some advisors and advocates may recommend an immediate move to certain organic solvent or solvent blends. There have been assertions that water-based products with the occasional use of soy methyl ester are the only permanent, long-term, safe approach to cleaning. We take issue with such assertions. 

Based on our decades of experience, there is no perfectly safe or environmentally bullet-proof cleaning process. Worker safety, product safety, and environmental safety are process-dependent, not just chemistry-dependent. Some processes might be “chemically safe” but need much more energy, or time, or floor space. Some replacement processes introduce new risks to worker safety, such as risks from flammable solvents. 

Employees using aqueous cleaning agents, even near-neutral cleaners, should use appropriate personal protective equipment like goggles and gloves; and they must be made aware of proper procedures regarding heated tanks. Further, as more information about a chemical or chemical blend becomes available, worker safety and environmental issues are more likely to be discovered. It would be unwise to adopt a supposedly safe cleaning process that is at best marginally effective.

Please, oh please, do not jump from the frying pan into the fire. Get in touch with us. Let’s have a conversation!

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