In April of 2024 the Environmental Protection Agency (EPA) finalized a rule banning most uses of methylene chloride (CAS RN: 75-09-2).
Read on to learn: Why they are banning this chemical? Why now? And how this will this impact laboratories, where methylene chloride is still critical to chemical research.
What is so bad about methylene chloride?
If you know anything about methylene chloride (common synonyms: dichloromethane, DCM, MC), you probably know that it is nasty stuff. Short-term exposures can affect the central nervous system, and chronic exposures can lead to liver toxicity, and cancer of the liver and lungs. If you have personally handled this chemical, then you may also know that it is highly volatile and quickly penetrates standard thickness disposable nitrile gloves, presenting challenges for protecting against exposure by both inhalation and dermal absorption routes. Like many highly potent chemicals, the properties that make it so hazardous are also what make it useful for commercial, industrial, and research purposes! It is a low boiling point, polar aprotic solvent, ideal for degreasing, paint stripping, aerosols, and a variety of other applications including synthesis, extraction, and purification in the laboratory.
The Occupational Safety and Health Administration (OSHA) has regulated methylene chloride to protect workers in General Industry since 1997 (29 CFR 1910.1052). In that standard, OSHA set a permissible exposure limit (PEL) for an 8-hour time-weighted average (TWA) exposure, a short-term exposure limit (STEL) for a 15-minute period, as well as an “action level,” which triggers the need for exposure monitoring and medical surveillance to ensure that exposures remain below those thresholds. This OSHA standard also includes requirements for establishing designated areas for methylene chloride use, hazard communication and training requirements for employees, and recommendations for safety controls to maintain methylene chloride concentrations below the permissible limits.
Why is the EPA banning methylene chloride now?
If this infamously hazardous material has already been regulated for decades, why is the EPA only now imposing this ban? The answer is, in short, because now they can!
In 2016, congress passed legislation to revise the EPA’s Toxic Substances Control Act (TSCA), granting the agency new powers and responsibilities for ensuring that “no chemical in U.S. commerce poses an unreasonable risk to human health or the environment.” Of 90 high-risk substances identified to be evaluated by the EPA, methylene chloride is among the first 10 for which they are conducting a mandatory risk review. In 2019, the EPA banned the use of methylene chloride and another chemical, N-methylpyrrolidone (NMP) (CAS RN: 872-50-4), for consumer and most types of commercial paint and coating removal. The agency focused on the paint and coating removal process first because of the high potential for exposure in this frequent, routine, and high-concentration usage. For evidence of that danger, just look at the worker fatality statistics, which show that between 1980 and 2018, of the 85 reported worker deaths related to methylene chloride exposure, 60 of them involved paint strippers.
The EPA’s revised methylene chloride risk evaluation in November of 2022, which evaluated an expanded set of conditions of use – unsurprisingly – determined that the chemical, “as a whole chemical substance, presents an unreasonable risk of injury to health under the conditions of use [evaluated].” In May of 2023, the EPA proposed their methylene chlorine regulation to ensure that this chemical would no longer present unreasonable risk to human health or the environment. After a period of public comment, the EPA finalized the rule in April of 2024, but as of the publication of this article in May of 2024, it has not yet been entered into the Federal Register.
Does this ban apply to laboratory use?
Although the rule does not impose a complete ban on the use of methylene chloride, it does prohibit it in most industrial, commercial, and consumer uses. The EPA, however, is allowing for “limited and controlled continued use in tandem with additional work protections for several purposes [. . .].” Among the list of 13 permitted uses is “industrial and commercial use as a laboratory chemical.”
The pre-publication of the rule explains that “laboratory settings are expected to be more conducive to the implementation of engineering controls such as fume hoods to ventilate vapors and adequately reduce overall exposure to methylene chloride consistent with the hierarchy of controls.” Of course, the use of methylene chloride in a laboratory setting will also be necessary for the analysis of the air samples that this rule requires!
How does the EPA rule compare with the OSHA standard for methylene chloride?
The EPA sought to keep their methylene chloride rule consistent with existing health and safety regulations for this chemical; however, it differs from the 1997 OSHA standard in some key ways. OSHA standards cover worker protection, but the EPA methylene chloride rule under TSCA applies to all “potentially exposed persons,” which is inclusive of not just workers, but also university students, volunteers, self-employed persons, and state and local government workers not covered by a state occupational health and safety plan.
The exposure thresholds in the EPA rule are also lower than OSHAs by an order of magnitude. EPA’s Existing Chemical Exposure Limit (ECEL) is 2 ppm as an 8-hour TWA, and 15-minute STEL is 16 ppm, whereas OSHA’s are 25 ppm and 125 ppm, respectively. Both agency’s use 1/2 the respective 8-hour TWA as an action level to trigger monitoring and medical surveillance.
Comparison of OSHA and EPA Exposure Thresholds
OSHA (1997)
EPA (2024)
8-hour TWA
PEL 25 ppm
ECEL 2 ppm
15-min STEL
125 ppm
16 ppm
Action Level
12.5 ppm
1 ppm
What will the requirements be for laboratories that continue to use methylene chloride?
Workplace Chemical Protection Program (WCPP)
While laboratories are still permitted to use methylene chloride, if they do so, they will be required to have a Workplace Chemical Protection Program (WCPP) in place. The WCPP requires monitoring to verify that the exposure thresholds are not exceeded, as well as record keeping requirements, and other measures such as dermal protection.
The requirement for the WCPP will take effect 180 days after publication of the final rule. This is when any affected organizations will be required to do their initial monitoring to establish a baseline of exposure for potentially exposed persons. Within 1 year of publication of the final rule, any necessary controls to reduce exposure are required to be in place. Because of the new, lower exposure thresholds set by the EPA, even organizations that are currently in compliance with the OSHA methylene chloride standard will need to perform these baseline monitoring activities. That is, unless they can provide EPA with data from within the past 5 years proving that methylene chloride levels cannot exceed the new ECEL action level or STEL.
These air samples are to be taken in the ambient air, so they will not take into account any respiratory protection devices that may already be in use.
The rule includes details for how to select appropriate representatives of individuals for conducting personal-breathing-zone air sample monitoring, and this guidance aligns with the existing approach in the OSHA standard for methylene chloride. Unlike the OSHA standard, however, EPA is requiring “initial” exposure monitoring to be repeated every 5 years for as long as the chemical remains in use at the facility.
If any of the results from the initial monitoring exceed the action level, STEL, or ECEL, then additional periodic monitoring will be required on frequencies of 3 months or 6 months depending on the results. Each potentially exposed person must also be informed of these results, and an exposure control plan (ECP) must document the actions taken to reduce exposures.
Exposure Control Plan
The EPA’s requirements for exposure control are meant to be flexible and will not prescribe specific methods or devices for reducing exposure. Rather, the EPA encourages the use of the recognized “Hierarchy of Controls” which emphasizes elimination and substitution of the hazard to be considered before engineering controls, administrative controls, and personal protective equipment are put in place. One of the requirements of the ECP is that it must document the process that was used to decide which controls are selected and justification for any less preferred approaches, such as requiring respiratory protection instead of using engineering controls to reduce the ambient concentration.
Although most of the requirements in the EPA rule pertain to respiratory exposures, it does also state that “gloves that are chemically resistant to methylene chloride” and “activity-specific training” must be included in the ECP for any task where dermal contact with methylene chloride is possible, assuming that the exposure cannot otherwise be avoided through substitution, elimination, and engineering controls.
Timeline for compliance for (Non-Government) laboratories
Required Action
Amount of time after date of publication of the final rule in the Federal Register
Establish initial exposure monitoring
360 days (and every 5 years, thereafter)
Ensure ECEL and STEL are not exceeded
450 days
If needed, sufficient respiratory protection provided to reduce exposures below thresholds
9 months (or 3 months after receipt of monitoring results)
Implement and document exposure control plan
540 days
What should laboratories do to prepare for the new requirements?
A suggested “Checklist to Prepare Laboratories for the Methylene Chloride” is included at the end of this article.
How do we know if we have any methylene chloride?
The first step should be to identify if your labs are storing and/or using methylene chloride. Utilize tools like SciSure's (formerly SciShield's) SDS QR Code to quickly access and manage Safety Data Sheets, ensuring up-to-date information and compliance with safety regulations. And if so, where, and how? If you have a trusted chemical inventory system, that could be as easy as searching the records for methylene chloride by name, CAS RN (75-09-2), and by any of the common synonyms (dichloromethane, DCM, MC).
If you are not confident in the completeness of the inventory, you can use messaging tools to target groups and individuals who may be storing or using the chemical. Instructing the lab inspection team to ask about this and to check chemical cabinets while in the lab space is another method for finding undocumented stocks of methylene chloride. Keep in mind that this chemical is often stored with other solvents, but it is not flammable and, thus, is not necessarily stored in the flammable liquids storage cabinets.
Although methylene chloride has been banned from paint strippers and other coating-removal products since 2019, now would also be a good opportunity to check products in maintenance and facilities shops or studios and replace any items that contain methylene chloride or N-methylpyrrolidone (NMP) (CAS RN: 872-50-4).
Can we just eliminate methylene chloride from the labs?
Although substitutions can be made for some methylene chloride uses, there may very well be lab operations where it will still be essential. In in Green Chem., 2008,10, 31-36 (DOI: 10.1039/BE) the Environmental, Health and Safety (EHS) group at Pfizer Global Research and Development recommend replacing methylene chloride with Ethyl Acetate/Hexane for chromatography and with Ethyl Acetate, MTBE, Toluene, or 2-MeTHF for extractions.
In Teledyne ISCO’s January 2023 “Dichloromethane (DCM) Substitutes and Selectivity” post, they suggest a 3:1 ratio of ethyl acetate to ethanol as a starting point for creating new methods without DCM for chromatography purification.
Chromatography and extraction are good targets for substitution, because they are two of the most common and high-volume laboratory tasks where methylene chloride is used.
How will we convince the lab personnel to make these changes?
You may encounter resistance as you try to remove this common solvent from the laboratory, as swapping for alternatives will require additional experimentation before appropriate substitutions can be validated. Discussing with laboratory leadership what will be realistic and beneficial before announcing any policies or mandates is critical to successful change management. It is important that your laboratory personnel are well aware of the hazards and the new requirements as soon as possible to get their buy-in and to enable a smooth transition.
One strategy for encouraging the use of alternative solvents is to enforce limits on the total permitted amount and/or the largest permitted container size of methylene chloride. By not instituting a complete ban, you enable critical processes to continue, while still promoting the use of substitutions by making it less convenient and more expensive to use the more hazardous chemical. Additionally, by limiting the largest container size (for example, to 500 mL), the chances of a large-volume spill or large-volume chemical transfers will be reduced.
Instituting a permit-for-use system, such is sometimes done with pyrophoric or other high-hazard materials, can also help with the ongoing monitoring of where and how the chemical is used while also checking that the proper training and safety controls are in place where needed.
Will we need to perform air monitoring everywhere methylene chloride is in use?
The EPA rule contains guidance on how to select representative “potentially exposed persons” for initial and periodic air monitoring, but figuring out which activities have the highest potential for exposure is the first step.
This may require first carefully observing operations where methylene chloride is used and talking to health-and-safety minded laboratory personnel about real practices. Keep in mind that the tasks with the highest short-term exposure may include set-up, start-up, or shut-down activities such as transfers from larger containers for filling reservoirs or creating stock solutions, combining purification fractions, emptying rotary evaporator traps, or pouring into waste containers.
When thinking about potentially exposed persons, remember to include any personnel who may be involved with waste consolidation operations, emergency response, and routine laboratory tasks. You may need to update emergency response plans to include new monitoring requirements and the use of supplied-air respirators for entry into methylene chloride spill areas.
What is next?
Now that the EPA has made available the pre-publication version of their proposed Methylene Chloride Regulation, chemical hygiene professionals can start communicating with lab personnel and their own health and safety teams to prepare for what is to come.
Although responsible lab safety programs will already have training and controls in place for management of this famously toxic chemical, this will be a time for revisiting past assessments, approvals, and results to consider whether ongoing use of methylene chloride is still warranted in light of the more stringent regulations.
The reality is, for many laboratory facilities, especially where basic chemical research, synthesis, and a wide range of analytical methods are everyday occurrences, it is unlikely that this chemical can be eliminated entirely. However, if health and safety teams lead with a collaborative mindset and a focus on risk assessment and mitigation, they will benefit from the creativity and problem-solving skills that laboratory workers and management can bring to the conversation.
After all, this will lay the groundwork for the chemical safety community to tackle compliance with many similar regulations in the coming years. At the time of writing this article, the EPA is currently evaluating 33 existing chemicals under the revised Toxic Substances Control Act to determine which others present unreasonable risk of injury to health or the environment; methylene chloride is simply the first to have a final published rule. The strategies and relationships developed now will set the precedent for successful responses to these future EPA chemical bans and restrictions.
Checklist to prepare laboratories for the methylene chloride regulation
Communicate and Plan Ahead
- Communicate with laboratories about methylene chloride hazards and new regulations
- Identify where methylene chloride is stored or in use
- Review any previous methylene chloride monitoring results to gauge which activities have already been assessed and whether those measurements indicate that the new, lower, thresholds are likely to be exceeded
Check Equipment
- Confirm that any equipment to be used for routine or emergency air-monitoring is calibrated and appropriate for measuring concentrations of methylene chloride to the level of detection necessary for the new exposure threshold values
- Confirm that local exhaust ventilation controls such as fume hoods and extractors are in service, inspected, and certified
Eliminate and Substitute Where Possible
- Work in close partnership with lab personnel to eliminate and substitute methylene chloride wherever possible— Consider instituting limits on total volumes or largest-container size to encourage the use of alternatives
- Identify where and how methylene chloride must still be permitted— Consider requiring a written approval (e.g., a permit) for any project or team where methylene chloride use will be allowed
Plan for Initial and Ongoing Compliance
- Work with a Certified Industrial Hygienist to create a monitoring plan for initial monitoring
- Document a Workplace Chemical Protection Program (WCPP)
- Update the Chemical Hygiene Plan and write a separate methylene chloride exposure control plan if needed
- Update initial and refresher training for chemical handling to highlight the health hazards of methylene chloride and any new approvals or other requirements that will be put in place
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