Methylene Chloride Facts No. 1
Exposure Monitoring Requirements

Occupational Safety and Health Administration

On January 10, 1997, the Occupational Safety and Health Administration (OSHA) issued a standard that lowered the limit on worker exposures to methylene chloride (MC). This new standard greatly reduces the chance of developing health problems from working in facilities that use MC.

Worker exposures to MC occur mainly through breathing its vapors. MC can also pass through workers' skin if it gets on their bodies or clothes. Occasionally, workers can swallow small amounts of MC if they don't wash their face and hands before eating, or if they eat in contaminated work areas. Short-term exposure to high levels of MC can cause dizziness, headaches, a lack of coordination, and irritation of the skin, eyes, mucous membranes, and respiratory system. Long-term exposure causes cancer in laboratory animals. Studies in workers suggest an association between MC exposures and certain types of cancer. OSHA considers MC to be a potential occupational carcinogen. Exposure to MC may also make the symptoms of heart disease (e.g., chest pains, angina) worse.

Monitoring employee exposures to MC enables employers to identify the sources of MC and select appropriate exposure controls. OSHA's MC standard requires that all facilities using MC monitor employee exposures. This fact sheet provides only general information on monitoring requirements and should not be considered to be a complete summary of the MC-related monitoring requirements. For specific exposure monitoring requirements, please refer to the OSHA MC standard (Title 29 of the Code of Federal Regulations, Part 1910.1052(d)).

General Requirements

If MC is used in the workplace, the employer must monitor employee exposure to MC to determine if any employee is being exposed to MC in excess of the permissible exposure limits (PELs): 25 ppm, as an 8-hour time-weighted average (TWA) PEL; and 125 ppm, as a 15 minute short-term exposure limit (STEL). Employers are required to conduct initial monitoring of airborne MC concentrations and to conduct periodic MC exposure monitoring for all tasks where employee exposures are above the action level (12.5 ppm, 8-hour TWA) or STEL. Validated monitoring methods include OSHA Method 1025 (available through the OSHA Occupational Chemical Database), badge monitoring, and other methods that meet the accuracy and precision requirements of the MC standard.

Initial Monitoring

Initial monitoring must be provided when MC is introduced into the workplace.

Initial monitoring is not necessary if:

  • Objective data, representing the highest MC exposure likely to occur during processing, use, or handling, show that MC cannot be released in concentrations above the action level or STEL;
  • Employee exposure monitoring was performed within 12 months prior to April 10, 1997, which satisfies the monitoring requirements and was conducted under conditions substantially equivalent to existing conditions; or
  • Employees are exposed to MC for fewer than 30 days per year and the employer uses direct-reading instruments to determine airborne levels of MC. In such cases, the direct reading instruments must provide immediate results which are sufficient to determine which measures are necessary to control employee exposure.

Periodic Monitoring

If initial monitoring shows employee exposures at or above the action level or STEL, employers must perform periodic 8-hour TWA or STEL monitoring as follows:

8-hour TWA monitoring:

  • Every six months if initial TWA monitoring results are at or above the action level but at or below the TWA PEL.
  • Every three months if initial TWA monitoring results are above the TWA PEL.
  • Periodic 8-hour TWA monitoring is not required if initial TWA monitoring results are below the action level.

STEL monitoring:

  • Every three months if initial STEL monitoring results are above the STEL.
  • Periodic STEL monitoring is not required if initial STEL monitoring results are at or below the STEL.

If two consecutive measurements, taken at least 7 days apart, show that exposure levels have decreased, employers may modify the monitoring requirements accordingly.

Additional Monitoring

Employers must perform additional monitoring if there is an indication that employee exposures have increased. Examples include changes in the production process, control equipment, or work practices that could increase exposure levels; and leaks, ruptures, or other equipment breakdowns.

Monitoring Specifications

In determining each employee's workplace exposure to MC, employers may take either:

  • Personal breathing zone air samples for each employee; or
  • Personal breathing zone air samples for one or more employees when the samples are representative of each employee's exposure.

Personal breathing zone air samples may be considered representative of an employee's 8-hour TWA and 15-minute short-term exposures if:

  • The employee(s) sampled are in the same job classification.
  • The employee(s) sampled work in the same area.
  • The employee(s) sampled work during the same work shift (if the employer can document that tasks and workplace conditions are similar during all work shifts, he/she only needs to determine the exposure level for one work shift).
  • The employee(s) sampled is expected to have the highest MC exposures of all employees in the group of employees represented by the samples collected.
  • For short-term exposures, samples are taken during operations likely to produce the highest 15-minute exposures.

Employee Notification

Employers are required to notify employees of all monitoring results, in writing, within 15 working days of receiving the results. If exposures are above the PEL or STEL, the employer must inform the employee of the corrective actions being taken.

OSHA's standard requires employers to allow affected employees or their designated representatives to observe any monitoring activities. Where such observations involve entry into areas where personal protective equipment (PPE) is necessary, the employer must provide and ensure the use of the appropriate PPE. In addition, the employer must ensure that observers follow all other applicable safety and health procedures.


Employers must establish and keep accurate records of all exposure monitoring data as well as the objective data used to support exemptions from initial monitoring requirements.

Exposure Monitoring Data:

Employers with 20 or more employees must keep exposure monitoring records for 30 years. The records must include information on:

  • Date of the measurement for each sample taken;
  • Monitored operation involving MC exposure;
  • Sampling and analytical methods used and evidence of accuracy.
  • Number, duration, and results of samples taken.
  • Type of PPE worn.
  • Name, social security number, job classification, and exposure levels (where representative samples are used, identify all employees represented by the data and indicate which employees were monitored).

Employers with fewer than 20 employees must also keep records for 30 years, but only need to include information on:

  • Date of measurement for each sample.
  • Number duration, and results of samples taken.
  • Name, social security number, job classification, and exposure levels (where representative samples are used, identify all employees represented by the data and indicate which employees were monitored).

Objective Data:

Objective data records must be kept as long as the employer relies on this data and include information on:

  • MC-containing material in question;
  • Source of the objective data.
  • Testing protocol, results, and/or analysis of the material.
  • Exempted operation and data supporting the exemption.
  • Other data relevant to the operations, materials, processes, or employee exposures covered by the exemption.

Additional Resources

Visit the On-Site Consultation Program page for information on how to request a free, confidential visit from a consultant to help identify ways to improve safety and health at your workplace.