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Methylene Chloride Standard FR 62:1494-1619
Occupational Safety and Health Administration (OSHA)

On January 10, 1997, OSHA issued its final standard lowering the workplace exposure limit for Methylene Chloride (MEC) from 500 parts per million (ppm) to 25 ppm as an 8-hour time?weighted average (TWA). In addition, it established a short-term (15-minute) exposure limit, or STEL of 125 ppm and an action level for a concentration of airborne MEC at 12.5 ppm (8-hour TWA)

This standard became effective on April 10, 1997 and has been phased in over a period of 3 years. The final action date of this standard is April 10, 2000. As of this date, all employers who’s facilities have Methylene Chloride present, are required to do the following:

1. Conduct air sampling of a representative sample of employees to determine the actual eight hour time weighted exposure level.

2. Notify employees within 15 working days after receipt of monitoring results.

3. If the level is less than 12.5 ppm, no further action is required.

4. If the results indicate exposures above the action level of 12.5 ppm (but below 25 ppm) you must provide for medical surveillance, employee training and record keeping of all employees exposed to MEC. You are also required to conduct air sampling every 3 months

5. If the results indicate exposures above 25 ppm, you must either remove MEC from the workplace or install engineering controls to lower the vapor levels.

How to Comply


The first step is to determine the exposure level of methylene chloride (MEC) to the employees in the facility. This must be conducted by the initial monitoring deadline as outlined above. According to the new standard, employers must conduct initial monitoring to determine their employees’ exposure to MEC by taking one or more personal breathing zone air samples. These samples must represent: a) Full shift exposure (8 hr Time Weighted Average-TWA) b) 15 minute Short Term Exposure Limit (STEL), for each shift, for at least one employee in each job class in each work area where MEC can be present.

Monitoring can be accomplished in house or by an independent testing service. There are two basic types of monitoring systems available. The simplest are badges that are worn by the employees on their collars for a typical 8-hour shift. These are similar to the radiation monitors worn by x-ray technicians. These particular monitors absorb the chemical vapor at the same rate as the subject. Once the test has completed the monitor is sent to a lab for analysis. The alternative for in house testing is by the use of glass detector tubes (Drager). These are glass tubes that act in a similar fashion to the badges. They are attached to a device that draws in a volume of sample air. This is normally conducted at strategic locations in the shop to simulate employees breathing zones. These tubes are also sent to a lab for analysis.

These testing devices can be purchased with the analysis pre-paid. It is essential to follow the manufacture’s instructions exactly to achieve an accurate test result. A list of manufactures and venders is included with this product bulletin.

Interpreting the Results

Minimal action is required If the monitoring results are at or below the OSHA guidelines (15 minute STEL under 125 ppm and airborne concentration below the action level of 12.5 ppm. All that is necessary is to document the test and keep it on file (If OSHA determines that the test results were inaccurate and/or incorrectly conducted – the employer may be considered in violation).

If the results exceed the action level of 12.5 ppm but are below the TWA of 25 ppm, and are within the STEL of 125 ppm, the employer must begin medical surveillance of the exposed employees by the dates outlined in the table. Additionally re testing must be conducted every 3 months until compliance is achieved

If exposure is in excess of the PEL of 25 ppm and/or the STEL of 125 ppm then action must be taken within 60 days to comply with the standard of 25 ppm. This can be by any reasonable means, i.e. Exhaust Station with air cleaning device, respirators, exhaust fans etc. The employer must then comply with the engineering controls deadline (permanent mechanical ventilation) by the required deadline date. This is to make the area safe for all employees. Additionally the medical surveillance and re-testing every 3 months must be conducted until full compliance is achieved.


A copy of the MEC rule and the OSHA compliance guide may be obtained from OSHA or by contacting the “Halogenated Solvents Industry Alliance (HSIA) at 202/775-0232. Additionally OSHA has a web site located at

Monitor types: 3M- 3520 Organic Vapor/ Monitor with back-up Section (Recommend Pre-Paid Analysis)

Lab Safety Supply Tel: 800/356-0783
3M Safety Division Tel: 800/896-4223

This is proprietary material copyright 2000 by Tekmar-Technical Marketing, Ltd.

Reproduction or use without written permission is strictly prohibited


© 2000 by Tekmar-Technical Marketing, Ltd.

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