DEPARTMENTS
INSTRUMENTATION
WILLIAM MILLS, PhD, MSc, CIH, CChem, FAIHA, is an associate professor in the College of Engineering and Engineering Technology at Northern Illinois University.
STEVEN JAHN, CIH, MBA, FAIHA, is past chair of AIHA’s Real-Time Detection Systems Committee, a technical advisor for Savannah River Mission Completion LLC, and president of Jahn Industrial Hygiene LLC.
JENNIFER L. MACLACHLAN is the managing director and co-owner of her family-owned and -operated real-time gas detection instrumentation manufacturing business, PID Analyzers LLC.
JACK DRISCOLL, the founder of HNU Systems Inc., first commercialized photoionization technology for real-time field detection and later applied it to the laboratory for gas chromatography applications. He is the head of R&D and technology at PID Analyzers LLC.
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Complying with EPA’s Methylene Chloride Rule
BY WILLIAM MILLS, STEVEN JAHN, JENNIFER L. MACLACHLAN, AND JACK DRISCOLL
Last year, EPA published regulations based on its findings that three halogenated solvents present unreasonable risk. In April, EPA finalized a rule for methylene chloride (MC), including the requirement for a Workplace Chemical Protection Program (WCPP). In December, EPA finalized a risk management rule that ultimately bans the manufacture (including import), processing, and distribution in commerce of trichloroethylene (TCE) for all uses but allows some processing and industrial and commercial uses to continue under a WCPP until the prohibitions come into effect. Also in December, EPA issued a final rule banning many uses of perchloroethylene (PCE) and requiring a WCPP and prescriptive controls for uses not prohibited.
These rules introduce existing chemical exposure limits (ECELs), which are eight-hour time-weighted averages; ECEL-short term exposure limits (ECEL-STELs); and ECEL action levels (ECEL-ALs). Table 1 summarizes the EPA and OSHA OEL values for these three chemicals.
Sampling or monitoring is discussed in each of the three rules. The regulations require that all sampling (for example, an integrated sample over a time period) or monitoring methods (a series of results obtained for less than 15 minutes) meet specific provisions for accuracy and precision.
The main focus of this article is the MC final rule, which allows a five-year delay in initial exposure monitoring for the characterization of limited-frequency uses. According to 40 CFR 751.109(d)(2)(ii), the five-year delay applies in the following circumstance:
Where potentially exposed persons are exposed to methylene chloride for fewer than 30 days per year, and the owner or operator has measurements by direct-metering devices which give immediate results and which provide sufficient information regarding exposures to determine and implement the control measures that are necessary to reduce exposures to below the ECEL action level and EPA STEL.
This allowance provides the opportunity for real-time detection systems (RTDS), also referred to as direct-reading instruments or DRI, to be deployed to allow a delay in (potentially more expensive) initial exposure monitoring; as workplace screening tools so that targeted interventions for better control may be initiated before more robust air sampling methods are deployed for exposure monitoring; or to provide exposure monitoring data to demonstrate compliance with the ECEL or ECEL-STEL.
Table 1. Occupational Exposure Limits for Three Halogenated Solvents
Click or tap on the table to view a larger version in your browser.
OBLIGATIONS FOR MC
This article establishes the logic of EPA’s WCPP and exposure control plan obligations that lead to monitoring in real time, what must be done to credit RTDS for verifying that exposures are “fewer than 30 days per year,” and available instrumentation to do so.
Why. EPA has established a complete ban on manufacture and downstream uses of MC with very limited allowances for continued and narrow uses that will sunset after ten years. Newly regulated workplaces include laboratories dependent upon MC as a solvent in many prescriptive methods. EPA declined to explore or acknowledge the established engineering controls found in research labs working to the OSHA 29 CFR 1910.1450 standard.
What. EPA has directed that monitoring requirements be codified in the WCPP. These occur as initial monitoring (40 CFR 751.109(d)(2)) and subsequent periodic monitoring (40 CFR 751.109(d)(3)). Such monitoring has accuracy obligations of plus or minus 25 percent of the ECEL (2 ppm) or EPA-STEL (16 ppm) and plus or minus 35 percent when between the ECEL-AL (1 ppm) and the ECEL (2 ppm). Repeat monitoring is established prescriptively based upon initial monitoring results. The implication is that similar performance is required for any RTDS.
Such monitoring must occur for all worker categories engaged from receipt of MC through consumption, waste generation, and packaging. As explained in A Strategy for Assessing and Managing Occupational Exposures, these worker categories may be assigned to similar exposure groups in accordance with conventional exposure assessment logic.
When. RTDS methods are best utilized to first verify a “green is clean” posture for work activities using MC in allowable ways defined in the regulation. Then, based on management analysis of conventional and expectedly infrequent work with MC (less than 30 days annually), targeted screening surveys with a properly configured instrument can be used either to demonstrate that hazardous releases resulting in possible worker exposures are not occurring or to define the timeline of hazardous releases. Screening needs to occur for all represented job functions and across all shifts so that exposure variability is incorporated into the compliance demonstration.
A compliance schedule requires that initial monitoring of workplaces still using MC be completed by May 5, 2025. A two-year extension is allowed for federal facilities and their contractors, according to EPA guidance (PDF).
Where. The screening allowance is applied to industries that meet one of the thirteen exemptions from the ban. For OEHS professionals, this is primarily expected to affect analytical laboratory businesses.
How. According to the MC regulation, “EPA is not precluding the use of any method, whether it constitutes a voluntary consensus standard or not, as long as it meets the performance criteria specified.” NIOSH has identified a number of RTDS with potential use in MC monitoring. AIHA’s document “Establishing a Process for the Setting of Real-Time Detection System Alarms” explains how to determine if a methodology is “fit for purpose.” An important part of this process is comparing the instrument or method detection limit to the OEL. A NIOSH researcher has commented, “Ideally the method detection limit (MDL) should be no greater than one tenth of the OEL.” For MC, this would be 0.1 ppm for the ECEL-AL, 0.2 ppm for the ECEL, and 1.6 ppm for the ECEL-STEL.
The simplest, least expensive DRI for MC are chemical indicating tubes. Unfortunately, typical detection limits using these tubes are higher than the ECEL. Field-portable RTDS based on the flame ionization detector have been used for organic vapor monitoring for more than forty years (see two reports from EPA as PDFs: one and two), but FID instruments require hydrogen gas and are bulky compared to other RTDS. A review of FID instrument specifications and discussions with vendors and users raises doubts about their ability to achieve detection limits in the 0.1–0.2 ppm range.
The photoionization detector utilizes ultraviolet light to ionize a molecule, which is pushed to a collector electrode where the current measured is proportional to a contaminant’s concentration. The most common PID lamp is 10.6 eV; however, MC’s ionization potential is higher than this, so an 11.7 eV lamp must be used. The 11.7 eV lamps in use have a much more limited service life (about 600–800 hours) and are more expensive than the 10.6 eV lamps. It is unclear whether current PIDs running 11.7 eV lamps would detect MC at an MDL of 0.1 ppm.
In theory, an electron capture detector would work due to its enhanced sensitivity for halogens, but the authors are not aware of any commercially available ECD systems that are not part of a laboratory gas chromatograph.
Infrared spectroscopy, notably Fourier transform infrared spectroscopy, is a well-established technique for organic and inorganic gases. FTIR is a more complicated and expensive RTDS that has been gaining in applications for IH monitoring with the advent of more portable units. Based on the authors’ review and discussions with several vendors, it is unclear whether current field-portable units can achieve the desired 0.1–0.2 ppm detection limit for MC.
The use of a field-portable GC is another possibility, but it is more complicated and expensive than typical RTDS used in OEHS.
Portable mass spectrometric methods, such as GC-MS or proton-transfer reaction mass spectrometry, offer the highest degree of accuracy and sensitivity for RTDS but are much more expensive and require considerably more training due to their complexity (PDF). Additional RTDS methods with potential applicability include photo acoustic spectroscopy, which has been used for detection of chemical warfare agents; cavity ring down spectroscopy; heated diodes, which are used for identifying halogenated refrigerant leaks (PDF); and metal oxide sensors (PDF).
Finally, while any monitoring method needs to be performed in a worker’s breathing zone, it may be possible to obtain a representative sample from outside of this zone, as long as conditions have not changed. It would be necessary to demonstrate that the atmosphere in the workplace is well-mixed—for example, multiple simultaneous samples or monitoring results will be needed in vertical and horizontal spatial distributions.
For those considering the use of RTDS for monitoring to meet the MC rule, the AIHA Real-Time Detection Systems Committee has produced several helpful documents. “Establishing a Process for the Setting of Real-Time Detection System Alarms” describes a process for identifying possible methods to implement and evaluate fit-for-purpose RTDS. One of the considerations in the selection of an RTDS will be available expertise; the document “Technical Framework: Guidance on Use of Direct Reading Instruments” can help. EPA requires that information about the monitoring method be recorded, including its accuracy. Specific requirements for recordkeeping are currently being developed by EPA, but useful information is provided in “Reporting Specifications for Electronic Real Time Gas and Vapor Detection Equipment” and the Sensor Evaluation and Specification Sheet (PDF) when completed for an RTDS.
ADJUSTING TO CHANGE
EPA's MC rule dramatically changes the health hazard status for businesses allowed to work under exemptions to the product ban. Screening technologies for real-time detection of conditions of the facility or behaviors of the workforce are available. OEHS professionals supporting these businesses should document their selected technology as meeting the regulatory method citations.
RESOURCES
AIHA: A Strategy for Assessing and Managing Occupational Exposures (2006).
AIHA: “Establishing a Process for the Setting of Real-Time Detection System Alarms” (2022).
AIHA: Technical Framework: Guidance on Use of Direct Reading Instruments (May 2022).
Air-Conditioning, Heating and Refrigeration Technology Institute: “Leak Detection of A2L Refrigerants in HVACR Equipment” (PDF, August 2017).
American Laboratory: “Industrial Hygiene Monitoring with a Variable Selectivity Photoionization Detector” (1979).
Annals of Occupational Hygiene: “Chemical Indicator Tubes for Measurement of the Concentration of Toxic Substances in Air: First Report of a Working Party of the Technology Committee of the British Occupational Hygiene Society” (April 1973).
Department of Homeland Security: “Field Portable Gas Chromatograph Mass Spectrometers-Assessment Report” (PDF, 2020).
Environmental Science and Technology: “Real-Time Measurements of Gas-Phase Trichloramine (NCl3) in an Indoor Aquatic Center” (June 2021).
EPA: “A Guide to Complying with the 2024 Methylene Chloride Regulation Under the Toxic Substances Control Act (TSCA)” (PDF, November 2024).
EPA: “Evaluation of Potential VOC Screening Instruments” in Incineration and Treatment of Hazardous Waste: Proceedings of the 8th Annual Research Symposium (PDF, February 1983).
EPA: “Soil Gas Sensing for Detection and Mapping of Volatile Organics” (PDF, 1987).
Federal Register: “Methylene Chloride; Regulation Under the Toxic Substances Control Act (TSCA)” (May 2024).
Federal Register: “Perchloroethylene (PCE); Regulation Under the Toxic Substances Control Act (TSCA)” (December 2024).
Federal Register: “Trichloroethylene (TCE); Regulation Under the Toxic Substances Control Act (TSCA)” (December 2024).
Gefahrst - Reinhaltung der Luft: “NIOSH Manual of Analytical Methods 5th Edition and Harmonization of Occupational Exposure Monitoring” (2015).
Journal of Exposure Science & Environmental Epidemiology: “The Application of PTR-MS and Non-Targeted Analysis to Characterize VOCs Emitted from a Plastic Recycling Facility Fire” (May 2024).
Journal of Occupational and Environmental Hygiene: “Evaluation of a Portable Gas Chromatograph with Photoionization Detector Under Variations of VOC Concentration, Temperature, and Relative Humidity” (April 2018).
Proceedings of SPIE: “Fast Detection of Chemical Warfare Agent Simulants by Photoacoustic Spectroscopy” (December 2024).
NIOSH: “Components for Evaluation of Direct-Reading Monitors for Gases and Vapors” (July 2012).
NIOSH: “Portable Gas Chromatography” in NIOSH Manual of Analytical Methods, 4th ed. (PDF, 1998).
NIOSH Manual of Analytical Methods: “Method 3800: Organic and Inorganic Gases by Extractive FTIR Spectroscopy” (PDF, 2016).
Optics Express: “Compact Photoacoustic Spectrophone for Simultaneously Monitoring the Concentrations of Dichloromethane and Trichloromethane with a Single Acoustic Resonator” (February 2022).