Laboratory Safety Manual - Chapter 22: Methylene Chloride Workplace Chemical Protection Program and Exposure Control Policy

University Policy

Title

Laboratory Safety Manual - Chapter 22: Methylene Chloride Workplace Chemical Protection Program and Exposure Control Policy

Regulatory Standard

The Environmental Protection Agency (EPA) issued a standard (40 CFR Part 751 Subpart B) to ensure proper protection of all workers exposed to Methylene Chloride (Dichloromethane or DCM). The standard applies to all forms and uses of methylene chloride as a laboratory chemical, including aqueous solutions, mixtures, and materials that can release it. The EPA existing chemical exposure limit (ECEL) methylene chloride is 2 parts per million (ppm) as an 8-hour time weighted average (TWA) and a short-term exposure limit (STEL) of 16 ppm in a 15-minute period. The EPA action level (AL) for methylene chloride is 1 ppm as an 8-hour TWA. The action level is the threshold for increased exposure monitoring and initiation of medical surveillance.

Scope

The Methylene Chloride Workplace Chemical Protection Program and Exposure Control Policy applies to all laboratories and laboratory personnel on campus.

Responsibilities

Principal Investigators

• Notify EHS of the use of methylene chloride and request approval for use as a laboratory chemical prior to purchase or continued use.
• Designate the use of methylene chloride in the individual Laboratory Safety Plan and address uses within the exposure control plan. Establish specifically designated areas for methylene chloride usage and storage.
• Ensure that laboratory personnel are aware of and trained in the hazards related to methylene chloride exposure.
• Ensure that laboratory personnel are utilizing the proper engineering controls, work practices, and personal protective equipment (PPE) to minimize methylene chloride exposure.

Laboratory Employees

• Ensure the laboratory worker registration form is selected for work with methylene chloride.
• Review the online Methylene Chloride training as required.
• Review and follow proper work practices, utilize proper engineering controls, and wear proper personal protective equipment to minimize methylene chloride exposure.

The Department of Environment, Health & Safety (EHS)

• Implement the UNC Methylene Chloride Workplace Chemical Protection Program and Exposure Control Plan.
• Conduct methylene chloride exposure monitoring.
• Review and provide feedback on individual Laboratory Safety Plans that identify methylene chloride use and recommend appropriate work procedures, controls, and personal protective equipment (PPE).
• Continuously update methylene chloride safety resources such as the online Methylene Chloride training and Methylene Chloride safety webpage.
• Annually review and update the UNC Methylene Chloride Workplace Chemical Protection Program and Exposure Control Policy.

University Exposure Control Plan

Health Effects

There are several health effects, both chronic and acute, that can result from exposure to methylene chloride. Acute inhalation and dermal exposure to methylene chloride can cause non-cancerous neurotoxic effects such as central nervous system depression (including loss of consciousness and respiratory depression that may result in coma and hypoxia).

Chronic inhalation and dermal exposure to methylene chloride can cause non-cancerous immune system compromise, irritation and burns, and liver effects such as liver toxicity (including vacuolization, necrosis, hemosiderosis, and hepatocellular degeneration). Chronic inhalation and dermal exposure, especially at high levels, can increase the risk of cancer.

Some adverse effects from high levels of methylene chloride exposure can be immediately experienced as dizziness and can result in sudden loss of consciousness or death. The EPA has documented fatalities linked to acute methylene chloride exposures, deeming it as a serious health threat for workers. Chronic lower-level exposures may result in long-term impacts that include cancer and liver damage.

Due to the acute and chronic symptoms that can occur with exposure to methylene chloride, both the EPA action level for methylene chloride monitoring and the best practices when working with methylene chloride are designed to keep methylene chloride exposures below the level where chronic symptoms may develop.

Hazard Assessment

Processes or occupational activities at UNC-Chapel Hill laboratories that may result in methylene chloride exposure include (but are not limited to): Instrument calibration and maintenance, chemical analysis, chemical synthesis, extracting and purifying chemicals, dissolving substances testing and evaluating methods, and similar activities, such as use as a solvent, reagent, analytical standard, or other experimental purposes.

Training

All employees that utilize methylene chloride must be trained in an understandable manner on its hazards and the available methods of protection before the initial job assignment and whenever a new procedure using methylene chloride is introduced into the work area. All employees must be trained on when PPE is necessary, what type of PPE is required, how to properly wear and adjust it, its limitations, and its care, maintenance, and disposal. Employees must demonstrate understanding and proper use of PPE before engaging in tasks requiring its use. All employees assigned to workplaces where methylene chloride concentration meets or exceeds 1 ppm (EPA AL) must be trained every five years to confirm their understanding of methylene chloride, its hazards, and the available methods of protection. Methylene Chloride training is available online.

Hazard Communication

All working bottles, mixtures, or solutions composed of methylene chloride should be labeled to identify the contents and hazards. Labels shall display the full chemical name (without abbreviations) and adhere to the Global Harmonized System (GHS) labeling standard, including hazard icons, a signal word, and a hazard description. Safety Data Sheets (SDSs) must be easily accessible to employees to allow them to review safety and health information on methylene chloride. Laboratory entrance signs should include hazard statements such as “Cancer Hazard” and “Highly Toxic” to alert individuals of the risks within the methylene chloride work areas. Some work areas may be required to establish “regulated work areas,” that include additional signage. See the section, “Regulated Work Areas,” for more information.

Medical Surveillance

Employee health complaints should be brought to the attention of the Principal Investigator and Safety Supervisor, and employees should seek immediate medical attention at the University Employee Occupational Health Clinic (UEOHC). Medical surveillance will be implemented for all employees exposed to methylene chloride at or above the AL or STEL. Occupational medical services are also available for employees who develop signs and symptoms of overexposure to methylene chloride and for employees exposed to methylene chloride in emergencies.

Exposure Monitoring

Exposure monitoring for methylene chloride is required in workplaces where concentrations may exceed the EPA ECEL or STEL limits. Monitoring includes initial, periodic, and additional assessments to evaluate and control exposure risks. Initial monitoring establishes baseline exposures under representative conditions, targeting the highest likely full-shift and short-term (15-minute) exposures. Samples must be collected in the personal breathing zone (PBZ) of potentially exposed individuals or representative samples under conditions that best represent the highest likely full-shift exposures. PBZ sampling data can apply across shifts if tasks and conditions are similarly documented, the person monitored is the most exposed individual, and all members of the similar exposure group have had an opportunity to observe the monitoring. Methods must achieve a 95% confidence level, with accuracy within ±25% for concentrations above the ECEL or EPA STEL and ±35% for concentrations between the action level and the 8-hour TWA ECEL.

Periodic monitoring is conducted to confirm ongoing compliance, with frequencies ranging from every 5 years to every 3 months, based on prior results. Monitoring can be paused under specific conditions, such as discontinued use of methylene chloride, but must resume if workplace circumstances change, such as increased production volumes or process modifications. Additional monitoring is required when changes in operations, equipment, or control measures potentially increase exposure or when employees exhibit symptoms of methylene chloride exposure.

If the laboratory has been active prior to October 2024 and had methylene chloride listed in their online chemical inventory or notified EHS of methylene chloride use, the laboratory should have coordinated initial monitoring and received a formal approval letter of use from EHS. If the laboratory was established after October 2024 or the laboratory has decided to implement the use of methylene chloride, the Principal Investigator is required to notify the EHS Chemical Safety Team via email (chemsafety@office.unc.edu) prior to purchase and use of methylene chloride.

Some laboratory work may qualify for exemptions from conducting initial monitoring for methylene chloride. The two conditions that a laboratory may be exempt from initial monitoring are:

1. If objective data generated during the last 5 years demonstrates methylene chloride is not released in the workplace environment at or above the ECEL action level and EPA STEL and with initial monitoring conducted within 5 years of that data.
2. If exposure to methylene chloride is less than 30 days per year with two conditions:
   1. Direct reading measurements must be taken in the environment to ensure levels are below the ECEL action level and EPA STEL.
   2. Appropriate controls must be put in place to ensure levels are below the ECEL and EPA STEL.

Laboratories are still required to notify EHS of the use of methylene chloride to identify if they fall within these exemption requirements for initial monitoring. Laboratories that fall under exemption requirements will still receive a formal approval of use document and will be required to update their laboratory safety plan with all required documentation and take the methylene chloride training. Laboratory personnel that fall under an exemption can request to see redacted monitoring data or the process of monitoring at any time. Laboratory personnel can request initial monitoring of methylene chloride use at any time, even if they fall under the exemption.

Periodic Monitoring Requirements

Periodic monitoring of methylene chloride exposure is based on the concentration levels found during initial monitoring.

If the concentrations are below the ECEL action level and at or below the EPA STEL (less than 1 ppm for an 8-hour average and 16 ppm for a 15-minute average), monitoring is required every 5 years.

If concentrations are below the ECEL but above the EPA STEL, ECEL monitoring is required every 5 years, while EPA STEL monitoring must occur every 3 months.

If the concentration is at or above the ECEL action level but below both the ECEL (1-2 ppm for an 8-hour average) and the EPA STEL (16 ppm for a 15-minute average), ECEL monitoring is required every 6 months.

If the concentration exceeds the EPA STEL but is still below the ECEL action level, ECEL monitoring occurs every 6 months and EPA STEL monitoring every 3 months.

If concentrations exceed the ECEL action level (above 2 ppm for an 8-hour average), both ECEL and EPA STEL monitoring must take place every 3 months

Changes to periodic monitoring requirements for methylene chloride are contingent upon specific conditions being met. If 2 consecutive monitoring events, conducted at least 7 days apart, show that potential exposure levels have decreased from above the ECEL to at or below the ECEL but remain at or above the ECEL action level, the frequency of monitoring can transition from every 3 months to every 6 months. Similarly, if 2 consecutive monitoring events indicate exposure levels have decreased to below the ECEL action level and at or below the EPA STEL, the monitoring frequency may shift from every 6 months to once every 5 years, with the second consecutive event establishing the new 5-year cycle. For individuals exposed less than 30 days per year, the use of direct-read monitoring is acceptable as well. For facilities that temporarily cease activities involving conditions of use requiring ECEL or EPA STEL monitoring, operators may skip the next periodic monitoring event if no relevant activities occur during the monitoring interval (3 or 6 months). However, documentation of the cessation must be maintained, and initial monitoring is required upon resuming such activities.

Table 1 below summarizes the monitoring and re-monitoring frequency requirements. 

Reporting Monitoring Results/Recordkeeping

Initial monitoring must occur before May 5, 2025, for existing laboratories that use methylene chloride, or within 30 days of introducing methylene chloride into the workplace. Principal Investigators are required to notify EHS prior to purchase of methylene chloride (See Exposure Monitoring for more information) All monitoring results must be accessible and clearly documented, shared with affected employees within 15 working days, and used to inform the development of exposure control plans and determine protective measures within the laboratory. Monitoring may be discontinued if two consecutive assessments show exposure consistently below action levels and the EPA STEL. Recordkeeping is essential for all monitoring events to ensure compliance and support regulatory audits. Laboratories will be required to establish individual exposure control plans within their online Laboratory Safety Plan. See Laboratory Exposure Control Plan for more information.

The disclosed monitoring results should outline the exposure limits, including the ECEL, action level, and EPA STEL, with a plain-language explanation of their significance. The results must indicate whether airborne concentrations exceed these thresholds. If limits are exceeded, the notice should describe actions taken to reduce exposure, provide details on required respiratory protections, and specify the quantity, location, and manner of methylene chloride use at the time of monitoring. Identified releases of methylene chloride should also be reported.

Principal Investigators must maintain ordinary business records for 5 years from their original creation that demonstrate compliance with the EPA’s methylene chloride ruling, such as bills of lading, invoices, and receipts. These records may be electronic or hard copy and may be stored centrally or dispersed across departments and research groups. EHS will keep records including annual laboratory safety inspections, chemical inventory updates, hazardous waste requests, and chemical fume hood maintenance and certification. These records are necessary in demonstrating that methylene chloride is being used or disposed of only within compliance of the ruling.

Regulated Areas

Within 3 months following receipt of their initial monitoring phase, the Principal Investigators must establish regulated areas where the concentration of airborne methylene chloride may exceed either the AL (1 ppm) or if the ECEL (2 ppm) or EPA STEL (16 ppm) was exceeded initially during monitoring but consecutive monitoring events showed that exposure levels have decreased to below the ECEL or EPA STEL. The Principal Investigator will be required to post and maintain legible signs bearing the following information at all entrances or access ways: Warning: Regulated Area for Methylene Chloride; Toxic and Potential Cancer Hazard; Authorized and Trained Personnel Only. A template of the sign can be found on the UNC Safety Signage webpage and is shown below in Figure 22.1. The Principal Investigator is required to restrict access to the regulated area to any person lacking training, appropriate personal protective equipment, or is otherwise unauthorized from entering. 

Figure 22.1. Example template of regulated area signage.

Under this program, long-term exposures to DCM will be kept below the ECEL and short-term exposures will be kept below the ECEL STEL. If consecutive monitoring events show that exposure levels remain at or above the ECEL or EPA STEL, the laboratory will be required to stop all use of methylene chloride. The laboratory will be restricted from using methylene chloride until a risk assessment is completed with EHS and consecutive monitoring events have shown that exposure levels that exposure levels are now below the ECEL or EPA STEL. UNC Chapel Hill will not allow the use of supplied-air respirators for laboratories if exposure levels are above the ECEL or EPA STEL.

Hierarchy of Controls

1. Elimination

The most effective method of protecting the user from methylene chloride is to eliminate the chemical from the workplace entirely. Removing methylene chloride from laboratories whenever possible can be done by changing work and research processes. However, methylene chloride remains essential in some laboratory and research settings due to its unique properties. It is widely used as a solvent in extractions, sample preparation, and chromatography because of its low boiling point, chemical stability, and the ability to dissolve a broad range of compounds. These qualities make it necessary for certain specialized research applications. Nevertheless, any non-essential or unused methylene chloride, or any methylene chloride kept for non-research use, must be submitted for disposal using the EHS Hazardous Materials Pickup Request Form.

2. Substitution

The second most effective method of protecting the user from methylene chloride exposure is via substitution. When considering a safer alternative, selecting a chemical that reduces the potential for harmful effects while not creating new risks is key to user safety. However, available substitutes for methylene chloride may be unsuitable for certain applications, like extractions, sample preparation, and cleaning processes, where methylene chloride's unique properties are necessary. Additionally, some substitutes may pose other hazards, such as increased flammability, toxicity, or reactivity, introducing new risks that must be carefully managed. See the list of alternative solvents on the EHS webpage for more information.

3. Engineering Controls

When it is not possible to eliminate or substitute methylene chloride, engineering controls are the next best method for reducing the risk of exposure. Engineering controls limit the concentration of airborne substances in the breathing zone of workers. Local exhaust ventilation in the form of a functioning chemical fume hood, glove box, snorkel, or other form of closed system should always be used whenever working with methylene chloride. Benchtop use of methylene chloride is only allowed after initial monitoring has been completed and shows that exposure levels are below the AL, ECEL, and EPA STEL.

4. Work Practices/Administrative Controls

The fourth most effective way to protect the user from methylene chloride exposure is by establishing work practices or administrative controls that reduce the duration, frequency, or intensity of methylene chloride. This could include work process training, reviewing procedures and hazard information, formulating standard operating procedures (SOPs) that include aspects such as requiring closed methylene chloride containers when outside of a chemical fume hood, developing work practices and SOPs for procedures involving methylene chloride, and ensuring that all individuals working with methylene chloride are appropriately trained. An additional administrative control or work practice may be implementing sufficient rest breaks. Principal Investigators may not use worker rotation as an administrative control to circumvent exposure limits. If possible, limit access to areas where there are risks of methylene chloride exposure due to its storage or use. Administrative controls also include the proper disposal of methylene chloride and storage of unwanted materials in waste containers. Ensure all halogenated waste containers are stored with appropriate ventilation, e.g., inside of a ventilated cabinet or designated waste area within the laboratory.

5. Personal Protective Equipment (PPE)

PPE is important in preventing employee exposure from splashes or other sudden contact with methylene chloride by creating a barrier between the user and the substance. PPE minimizes the potential for employee exposure, but unlike elimination, substitution, engineering, and administrative controls, it does not reduce ambient methylene chloride exposure levels. Therefore, PPE should only be used as a supplement to elimination, substitution, engineering, and administrative controls. Recommended PPE includes chemical resistant gloves, eye protection, long sleeves, closed-toe shoes, lab coats, and in some cases, respiratory protection. Not all types of dermal protection are effective against methylene chloride; recommended gloves include those made from polyethylene vinyl alcohol (PVA), ethylene vinyl alcohol (EVA), butyl, or linear low-density polyethylene (LLDPE). Viton and Silvershield are also satisfactory options. While PVA and butyl gloves can potentially cause a loss of dexterity due to the fit of the glove, another recommended glove combination can be used to improve dexterity. Ansell 02-100 with wearing Ansell 92-600 over the 02-100 pair, can be effective in both chemical resistant and for improving dexterity. For small volumes (100mL or less), short periods of time, and low-risk of exposure procedures can utilize the method of double-gloving with nitrile or neoprene gloves (e.g., Ansell 92-600 or Ansell 93-260) may be acceptable. Contact EHS if you may have procedures that apply to this.  For emergency response personnel only, supplied-air respirators (SAR) can be used for methylene chloride. Employees must receive training, fit testing, and medical evaluation before being permitted to wear a properly fitted SAR.

Housekeeping and Spill Response

In areas where methylene chloride is utilized and spills may occur, provisions must be made to contain spills, decontaminate the work area, and dispose of the waste. Employees cleaning up spills must be properly trained and wear suitable PPE and appropriate clothing. For small spills (<100 mL aqueous solution), isolate the hazard area, deny entry to unauthorized individuals, contain the spill with absorbent materials, and place spill materials within an airtight container until picked up by EHS. For larger spills (>100 mL aqueous solutions) or emergencies where the ECEL or EPA STEL may be exceeded, evacuate the area, deny entry to all individuals, and call EHS (919-962-5507) during work hours or 911 after hours.

Emergency Situations

A written plan should be in effect for regulated areas and work areas that are known to use large volumes of methylene chloride or are more likely to have a spill based on the work process. The emergency plan should be communicated to employees and posted in an accessible area. The EHS Emergency Response/HazMat Team and other emergency responders should be informed of the regulated areas and work areas in the event they are called to respond to an incident.

Laboratory Exposure Control Plan

Laboratories may not utilize methylene chloride until an approval letter has been sent from EHS and the Laboratory Safety Plan has been approved with all requirements outlined in the laboratory exposure control plan and approval letter.  The laboratory will receive an approval letter from EHS after completing initial monitoring requirements or may receive an approval letter if they fall under exemptions to monitoring requirements (See Exemption to Initial Monitoring for more information). The approval letter will contain all redacted exposure monitoring results conducted for the laboratory regarding each process, any recommendations required from the exposure monitoring, and instructions on updating the laboratory safety plan.

Each laboratory that uses methylene chloride is required to establish a laboratory exposure control plan. Instructions and requirements for a laboratory exposure control plan are outlined below.

In Schedule B of the Laboratory Safety Plan under “Safety Procedures and Rules,” include:

• Why dichloromethane is a necessary solvent to be used in the laboratory
  • The reason why should include why it cannot be eliminated or substituted by another solvent.
• Description of all uses of dichloromethane within the laboratory including
  • All processes and procedure using dichloromethane
  • Amounts of dichloromethane used
  • Engineering controls utilized to prevent exposure
  • Laboratory specific training that is required for us
  • Recommendations made from the approval report
• Describe all personal protective equipment utilized with dichloromethane
  • Including specific glove type (note that nitrile gloves are not recommended; butyl and poly-vinyl alcohol are recommended)

Related Requirements

External Regulations 

• 40 CFR part 751, subpart B (Methylene Chloride Regulation under the Toxic Substances Control Act)
• 29 CFR 1910.1052 (Toxic and Hazardous Substances – Methylene Chloride)

Contact Information

Primary Contact

Name: Catherine Brennan

Title: Executive Director, Department of Environment, Health & Safety

Telephone: 919-843-5331

Email: crbrennan@ehs.unc.edu

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