Assessing occupational mercury exposures during the on-site processing of spent fluorescent lamps.

Introduction

Fluorescent lamps are an efficient, and thus commonly used, source of lighting in office buildings, retail establishments, and schools (U.S. Environmental Protection Agency [U.S. EPA] Office of Solid Waste, 1998). In order to operate efficiently, all fluorescent lamps contain some amount of mercury. Typically, fluorescent lamps consist of a sealed glass tube coated with a powdered phosphor material and filled at low pressure with argon gas and mercury vapor. Tungsten coils coated with an electron-emitting material form electrodes at either end, and when voltage is applied, electrons pass through the tube, striking the argon atoms and releasing more electrons. These electrons strike the mercury atoms, causing the orbital electrons to move to an excited state, and upon relaxation, the mercury atoms emit ultraviolet light, which strikes the phosphor, causing it to fluoresce and produce visible light (U.S. EPA, Control Technology Center, 1994).

When fluorescent lamps are discarded or recycled, and subsequently broken, mercury may be released into an occupational setting or the surrounding environment, resulting in possible adverse health or environmental effects. When mercury is released into the environment, it can be converted into organic forms such as methylmercury and can bioaccumulate through the food chain (Raposo & Roeser, 2001). All forms of mercury are toxic to humans, adversely affecting the endocrine and nervous systems (Aucott, McLinden, & Winka, 2003).

According to U.S. EPA, 881 million fluorescent lamps were projected to be discarded in 2003, and the National Electrical Manufacturers Association (NEMA) estimated that 661 million lamps were discarded in 2000 (NEMA, 2000; U.S. EPA Office of Solid Waste, 1998). While U.S. EPA and NEMA numbers for lamps disposed on an annual basis vary somewhat, the likely true number of lamps discarded is still on the order of several hundred million per year and will probably continue to increase as U.S. EPA promotes the use of fluorescent lamps for energy conservation measures. In supporting the use of fluorescent lamps through its "Green Lights Program," U.S. EPA recognized NEMA's claim that mercury released into the environment by lamp disposal is significantly offset by energy conservation since the reduction in mercury emitted from anthropogenic sources, such as coal-fired power production, would be reduced by the use of fluorescent lamps (U.S. EPA Control Technology Center, 1994).

Historically, the processing of spent lamps involved removal of the spent lamp from the light fixture and either placement in the municipal waste stream or accumulation in fiberboard boxes for possible recycling. Modifications to applicable hazardous waste regulations and demands for spaces occupied by large volumes of spent lamps combined to make the on-site processing of spent lamps a desirable alternative. While on-site processing (inclusive of spent-lamp handling, movement, crushing, and residue collection) can help prevent the introduction of mercury into the municipal waste stream, the process represents a possible source of mercury exposure to workers. This circumstance is of particular concern because on-site lamp processing is rarely carried out in facilities specifically designed for this operation. A characterization of the possible exposures inherent to these on-site operations would be useful to determine if excessive occupational exposures were possible.

Universal Waste Rule

To reduce the amount of mercury potentially released into the environment by fluorescent lamps, U.S. EPA added used mercury-containing lamps to the list of "universal wastes" on July 6, 1999 (Hazardous Waste Management System, Modification of the Hazardous Waste Program, Mercury-Containing Lamps Proposed Rule, 1994). Universal wastes are hazardous waste that are widely generated and include used batteries, pesticides, mercury-containing thermostats, and paint and paint-related wastes. This reclassification essentially modified the Resource Conservation and Recovery Act (RCRA) regulations as they applied to storage time limits, transportation and manifesting requirements, and collection locations for used lamps. According to U.S. EPA, used lamps previously regulated under RCRA as hazardous waste were frequently mismanaged during storage and transport, as well as improperly disposed of in municipal landfills (Hazardous Waste Management System, Modification of the Hazardous Waste Program, Mercury-Containing Lamps Final Rule, 1999). Improper disposal under RCRA hazardous waste regulations was due to the large number of fluorescent lamps in use and to a lack among many generators of familiarity with environmental regulations and mercury hazards associated with used fluorescent lamps. Further adding to the improper-disposal problem was the exemption for conditionally exempt small-quantity (CESQ) generators producing less than 100 kilograms of hazardous waste per month. The CESQ exemptions from RCRA Subchapter C disposal requirements allowed these entities to legally place their used lamps in state-approved industrial waste or municipal landfills. Under the new universal waste designation, all generators of used lamps exceeding U.S. EPA's toxicity characteristic leachate procedure (TCLP) value for mercury of 0.2 mg/L are required to manage used lamps as universal waste (Standards for Universal Waste Management Rule, 2000). The TCLP values are derived for purposes of controlling environmental releases and are not directly related to possible occupational exposures. Used lamps designated as universal waste must be shipped to an authorized destination facility for disposal or treatment such as recycling.

U.S. EPA divided generators of used lamps into two categories: small- and large-quantity handlers of universal waste. Small-quantity handlers of universal waste are defined by U.S. EPA as generators of universal waste or owner/operators of facilities that receive universal waste from other handlers that do not accumulate more than 5,000 kg (11,000 pounds) of any universal waste, combined, at any time. Universal waste may be accumulated on site for a period of one year from the generation date, and all off-site waste shipments must be to another universal-waste handler, destination, or recycling facility, or to a foreign destination. Small-quantity handlers of universal waste are not required to notify U.S. EPA about waste-handling activities or maintain records of off-site shipments; however, prohibitions restricting disposal, treatment, and dilution exist (Standards for Universal Waste Management Rule, 2000). In addition, small-quantity handlers of universal waste are required to inform employees managing universal waste of proper handling and emergency response procedures specific to the types of waste managed.

Large-quantity handlers of universal waste are defined by U.S. EPA as generators of universal waste or owner/operators of facilities that receive universal waste from other handlers that accumulate more than 5,000 kg (11,000 pounds) of any universal waste combined. Large-quantity handlers of universal waste must notify U.S. EPA of waste-handling actives, obtain a U.S. EPA registration number, and train employees about waste management and emergency response procedures. Records of off-site shipments must be kept for three years, and as with small-quantity handlers of universal waste, the waste can be stored on site for a period of up to one year (Standards for Universal Waste Management Rule, 2000).

Recycling Programs

One of U.S. EPA's goals for regulating used lamps as universal waste was to make it easier and more cost-effective for handlers to recycle used lamps. Used lamps could be accumulated on site, placed in containers or crushed on site, and then shipped to a recycling facility, where the mercury would be recovered in a retort facility, with the purified mercury to be resold on the open commodities market (U.S. EPA, Control Technology Center, 1994). According to NEMA, approximately 25 percent of the lamps discarded in the United States are currently recycled, and U.S. EPA projects that recycling rates for used lamps will reach 50 percent by 2007 (NEMA, 2000). By contrast, a study (Raposo & Roeser, 2001), has reported lower levels of used-lamp recycling and greater landfill disposal rates in Brazil, where it is not required that used lamps be managed in a specific manner as universal or hazardous wastes.

As the practice of recycling used fluorescent lamps has become more prevalent, many generators of used lamps have implemented comprehensive fluorescent-lamp recycling programs, even though most modern lamps contain lower amounts of mercury that generally do not exceed the TCLP values and can legally be disposed of in municipal landfills. As described in a NEMA position statement, lamps with green markings or designations contain reduced mercury, do not exceed TCLP values for mercury, and do not have to be managed as universal wastes (NEMA, 2002). These limits were not derived for the purposes of controlling possible occupational exposures, however, so the mercury contained within the lamps continues to represent a possible source of occupational exposure if released.

Used-lamp generators seeking to reduce space requirements and costs associated with recycling of fluorescent lamps are exploring alternative options such as on-site crushing of lamps into 55-gallon drums prior to shipment to a mercury-recycling facility. The process of crushing used lamps on site provides an approximately 80 percent reduction in volume and can reduce transportation cost associated with shipping universal waste to a recycling facility. An important consideration for universal-waste handlers wishing to crush lamps on site is the ban on treatment established by the U.S. EPA under RCRA Subtitle C (Standards for Universal Waste Management, 2000). Many states have adopted the federal universal-waste rules for used lamps and have been authorized to replace the term "treatment" with "processing." Used-lamp generators are allowed to process or crush lamps on site; however, treatment and dilution are prohibited. This prohibition on dilution or treatment effectively requires all crushed lamps, regardless of TCLP results, to be managed as universal wastes. In addition, crushing of lamps is permitted on site only with crushing systems that have demonstrated mercury exposure to be less than 0.05 mg/[m.sup.3] on the basis of an 8-hour time-weighted average of samples taken at breathing-zone height near the crushing system. In general, facilities that use lamp crushers rely on the equipment manufacturers for occupational and environmental exposure data, an arrangement that does not take into account two key issues: possible exposures during the handling stage of processing and the effects of work site ventilation or lack thereof.

Occupational Mercury Exposure Potential

In the processing of used fluorescent lamps, elemental mercury vapor may potentially be released at levels that may exceed occupational exposure standards (U.S. EPA Control Technology Center, 1994). The Occupational Health and Safety Administration (OSHA) has established a permissible exposure limit of 0.05 mg/[m.sup.3] during an 8-hour workday for mercury vapor (U.S. Department of Labor, OSHA, 1991). The American Conference of Governmental Industrial Hygienists (ACGIH) has established a threshold limit value for inorganic-mercury-vapor exposure of 0.025 mg/[m.sup.3] averaged over an 8-hour work shift (American Conference of Governmental Industrial Hygienist, 2005).

U.S. EPA's Office of Solid Waste has considered mercury in the vapor phase and the phosphor powder in estimating potential emission and exposure rates. Mercury adsorbed to the glass and end caps was considered sufficiently bound to be omitted as a possible emission or exposure source (U.S. EPA Office of Solid Waste, 1998). A 2003 study by Aucott, McLinden, and Winka reported release rates of 3 to 8 mg of elemental mercury vapor when a single low-mercury lamp is broken; the study also reported that elevated levels of mercury may exist in the vicinity of recently broken lamps (Aucott et al., 2003). Typically, 750 to 1,200 used lamps can be crushed into one 55-gallon drum with commercially available drum-top lamp crushers. This number of crushed lamps could release 2,250 to 9,600 mg of elemental mercury vapor, which, if not properly captured, could constitute a source of exposure for operators of lamp-crushing equipment. In general, commercially available lamp-crushing units may have no emission control systems other than a fitted lid, or they may be fitted with vacuum and charcoal-filtering attachments to reduce possible occupational exposures during crushing operations.

Table 1 defines the terms, acronyms, and regulations that are used in this manuscript.

Methods

To assess the possible mercury exposure encountered by operators during the on-site processing of spent lamps, monitoring was conducted during processing operations, which included lamp handling, lamp crushing, and drum closure operations. The lamp crusher used in this evaluation was a commercially available model, consisting of a fixture that fits on top of a 55-gallon drum. The unit has a tubular chute into which lamps are fed, and it is equipped with a vacuum for maintaining negative pressure inside the drum; the exhaust is fitted with a HEPA and activated-carbon filter. A worker equipped with protective work gloves and eyewear removes spent lamps from shipping or collection containers, usually cardboard boxes, and feeds lamps through the inlet tube of the unit, where the lamps are struck by a rotating chain and broken, and the contents are pulled into the drum by negative pressure created by the vacuum.

Four processing sessions were conducted, two in an open outdoor work environment and two in an enclosed work area. Each processing session lasted about 4 hours and involved the processing of approximately 800 4-foot lamps. Within each set of 800 lamps, approximately half were standard fluorescent lamps (as indicated by silver end tips, reflecting an average mercury concentration of 33.14 mg per lamp) and half were low-mercury-content lamps (as indicated by green end tips, reflecting an average mercury concentration of 25.19 mg per lamp) (Hazardous Waste Management System, Modification of the Hazardous Waste Program, Mercury-Containing Lamps Proposed Rule, 1994). This distribution was selected as a compromise designed to reflect real processing situations because facilities generally process both silver- and green-tip lamps. The total number of spent lamps available for processing was also too low to allow processing sessions to be dedicated for each type, or to achieve adequate sample collection times.

At the end of the lamp-crushing phase of the process, the drum lid fixture was removed and the particulate filter exhaust removed from the exhaust and placed inside the drum along with the crushed lamp contents. The drum was then fitted with a standard drum lid and sealed. The basic methodology used for the assessment is derived from previously published technical reports (Singhvi, Turpin, Kalnicky, & Patel, 2001; OSHA, 1991; OSHA, 1989). During the entire process, passive dosimetry for mercury vapor was employed to collect personal and area samples. The authors collected the personal sample by placing the dosimeter on the collar of the lamp crusher operator during crushing. The area sample was taken 3 feet away at a height of 5 feet. Sampling was conducted in accordance with OSHA Method Number 140. The method has a quantitative detection limit of 0.004 mg/[m.sup.3] for elemental mercury vapor for a 240-minute sampling period (U.S. Department of Labor, OSHA, 1991).

Particulate mercury also was actively monitored during lamp-crushing activities by means of a mercury-containing ester filter and a calibrated personal sampling pump. These active samplers, placed in the same locations as the passive dosimeters, were intended to capture any particulate mercury exposures from the phosphor powder that might be released if any lamps were chipped or broken outside of the lamp-crushing unit. The active-sampling method used for this study, OSHA Method No. 145, has a minimum detection limit of 0.002 mg/[m.sup.3] (U.S. Department of Labor, OSHA, 1989), which is sufficiently lower than the most conservative 8-hour time-weighted average (TWA) exposure limit of 0.025 mg/[m.sup.3] published by the ACGIH.

The passive dosimeters used hopcalite as the solid sorbent, which was digested with nitric and hydrochloric acid. The analytical procedure requires that mercury in the sample be reduced to an elemental form by the addition of stannous chloride, followed by analysis with a cold-vapor atomic absorption spectrophotometer (U.S. Department of Labor, OSHA, 1991). The active samples were taken on an 8-[micro]m-pore-size mixed-cellulose ester filter with a personal sampling pump calibrated to approximately 1.0 l/min. The filter was digested with nitric acid, sulfuric acid, potassium permanganate, and hydroxylamine, then reduced to a mercury vapor by addition of stannous chloride; analysis was conducted with a cold-vapor atomic absorption spectrophotometer (U.S. Department of Labor, OSHA, 1989). All samples were analyzed by an American Industrial Hygiene Association (AIHA)-accredited laboratory.

The active- and passive-sample results were evaluated as exposures during the sampling trials, as well as converted into 8-hour time-weighted averages and compared with the OSHA and ACGIH inorganic-mercury exposure standards of 0.05 and 0.025 mg/[m.sup.3], respectively, according to the accepted assumption that no additional mercury exposures occurred during the remaining 4-hour workday period. Active- and passive-sample results from the two trials were also compared with each other through descriptive statistics and two sample t-tests to determine if any statistical differences existed between the unventilated and indoor trial locations.

In addition to the sampling described above, a Jerome Model 431 mercury analyzer was used to determine real-time mercury vapor concentrations during each of the four trials. Two points were sampled near the lamp-crushing unit: 1) the breathing zone around the lamp inlet tube and 2) a point near the area samples, 3 feet away at a height of 5. Readings were taken with the Jerome analyzer before any lamps were crushed in order to establish a baseline at 30-minute intervals during crushing operations.

Results

The results from the three types of monitoring during the four processing runs are shown in Table 2. in units of mg/[m.sup.3], as 8-hour time-weighted averages (TWAs). For the purposes of TWA calculations, it was assumed that no additional exposures had occurred outside the time frames established for lamp-processing runs. The average length of time to process the 800 lamps in each processing run was approximately 3.5 hours. An average of 30 lamps were cracked or broken during the handling stage of each processing run before being placed into the crusher.

The mercury vapor concentrations detected in the enclosed setting, according to both personal- and area-exposure measurements, were found to exceed the OSHA 8-hour TWA permissible exposure limit (PEL). This was not the case for the samples collected in the outdoor setting. The results of the t-test comparison for statistically significant difference indicated that when considered in aggregate, the results from both the personal and area mercury vapor monitoring were different in the enclosed setting than in the outdoor setting, at the p = .05 level.

All of the particulate samples collected for mercury content exhibited levels below the established OSHA limit, and no statistically significant difference was noted between the results obtained in the enclosed setting and those obtained in the outdoor setting. The low levels of mercury detected from the particulate monitoring suggests that the particulate releases inherent to lamp processing were not a significant source of mercury exposure.

The results of the Jerome monitoring indicated that some TWA limits were exceeded both in the enclosed and in the outdoor settings, but no statistically significant differences were noted upon application of t-test analysis. These results are presumed to be due to the comparatively short monitoring intervals (30 minutes), combined with peaks in concentration levels, that occurred because lamps were broken upon handling. This situation typically arose when a lamp broke prior to or during insertion into the lamp-crushing device.

Discussion

The results from the monitoring of a controlled series of lamp-processing operations indicate that, in some situations, mercury exposures in excess of the established OSHA standard can occur. Of particular note were the differences between results from enclosed settings and outdoor settings. It was also notable that OSHA exposure levels were exceeded even when half of the lamps processed were of the "low-mercury-content" variety.

On the basis of the findings that resulted from this monitoring, some recommendations for prudent processing of spent fluorescent lamps can be identified:

* Consider all of the potential hazards inherent to the process. Although the project reported here focused on the assessment of possible mercury exposures, mercury exposure certainly is not the only potential health and safety hazard associated with the processing of spent lamps. Given the number of lamps that cracked or broke during processing, protective equipment is needed to protect the eyes, face, hands, and skin. At a minimum, safety goggles and a face shield should be employed, along with thick work gloves and outer garments that protect the arms, neck, and upper legs. Consideration also should be given to the ergonomics associated with the handling of boxes and drums. Respiratory protection may be considered as well, but use of these devices entails additional requirements for fitting, maintenance, and education.

* In any workplace safety assessment of on-site lamp processing, the entire process should be considered, not just the crushing phase. The on-site processing of lamps includes several handling steps that likely contribute to possible elevated exposures. Two steps warranting particular attention are 1) lamp handling, during which breakage can occur, and 2) drum lid removal and associated filter change.

* Keep in mind that although fluorescent lamps contain only a small amount of mercury, the potential for mercury overexposures still exists, depending on the number of lamps processed and the subsequent concentrations of residues prior to recycling. (Even the newer lamps with green markings contain mercury, albeit at lower amounts.)

* Given the elevated mercury exposures associated with processing used lamps in an enclosed work environment, a simple way to reduce employee mercury vapor exposures is to perform lamp processing and crushing in well-ventilated or outdoor work locations. If this option is not possible, strict attention should be paid to the efficacy of ventilation systems within the enclosed area being used.

* Consistent with good industrial-hygiene practice, periodically monitor or sample the work environment during lamp-processing and -crushing activities to ensure that the lamp-crushing unit is operating efficiently and that permissible exposure limits are not exceeded.

Corresponding Author: Alan Lucas, Manager, Environmental Protection, The University Texas Health Science Center at Houston, 1851 Crosspoint Ave., OCB 1.330, Environmental Health & Safety Department, Houston, TX 77054. E-mail: [e-mail].

REFERENCES

American Conference of Governmental Industrial Hygienists. (2005). Threshold limit values for chemical substances and physical agents and biological exposure indices (Publication No. 0105). Cincinnati, OH: Author.

Aucott, M., McLinden, M., & Winka, M. (2003). Release of mercury from broken fluorescent bulbs. Journal of Air Waste Management Association, 53(2), 143-151.

Hazardous Waste Management System, Modification of the Hazardous Waste Program, Mercury-Containing Lamps, 59 Fed. Reg. 39288 (proposed July 27, 1994) (to be codified at 40 C.F.R. pts. 260, 261, and 273). Retrieved August 18, 2003, from http://frwebgate5.access.gpo.gov/cgi-bin/waisgate.cgi?WAISdocID=218403360459+2+0+0&WAISaction=retrieve.

Hazardous Waste Management System, Modification of the Hazardous Waste Program, Mercury-Containing Lamps [Final Rule], 64 Fed. Reg. 36466 (July 6, 1999) (to be codified at 40 C.F.R. pt. 260, 261, 264, 265, 268, 270, and 273). Retrieved August 18, 2003, from http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=1999_register&docid=fr06jy99-22.pdf.

National Electrical Manufacturers Association. (2000). Environmental impact analysis: Spent mercury-containing lamps. Rosslyn, VA: Author.

National Electrical Manufacturers Association. (2002). Position statement of the lamp section on green marking of lamps. Rosslyn, VA: Author.

Occupational Safety and Health Administration. (1991). Mercury vapor in workplace atmospheres inorganic Method No. 140. Retrieved August 17, 2003, from http://www.osha.gov/dts/sltc/methods/inorganic/id140/id140.html.

Occupational Safety and Health Administration. (1989). Particulate mercury in workplace atmospheres Method No. 14. Retrieved August 24, 2003, from htpp://www.osha.gov/dts/sltc/methods/inorganic/id145/id145.html.

Raposo, C., & Roeser, H.M. (2001). Contamination of the environment by the current disposal methods of mercury-containing lamps in the State of Minas Gerais, Brazil. Waste Management, 21, 661-670

Singhvi, R., Turpin, R., Kalnicky, D.J., & Patel J. (2001). Comparison of field and laboratory methods for monitoring metallic mercury vapor in indoor air. Journal of Hazardous Materials, 83(1-2), 1-10.

Standards for Universal Waste Management, 40 C.F.R. [section] 273 (2000).

U.S. Environmental Protection Agency Control Technology Center. (1994). Evaluation of mercury emissions from fluorescent lamp crushing (EPA-453/R-94-018). Washington, DC: U.S. Government Printing Office.

U.S. Environmental Protection Agency Office of Solid Waste. (1998). Mercury emissions from the disposal of fluorescent lamps, revised model, final report post-OMB review. Retrieved August 17, 2003, from http://www.epa.gov/epaoswer/hazwaste/id/merc-emi/mercpgs/emmrpt.pdf.

Alan Lucas, M.S., C.H.M.M.

Robert Emery, Dr.PH., C.H.P., C.I.H., C.S.P., R.B.P., C.H.M.M., C.P.P., A.R.M.

TABLE 1 Terms, Acronyms, and Regulations Related to Spent Fluorescent
Lamps

Term, Acronym,
or Regulation    Definition

ACGIH            American Conference of Governmental Industrial
                 Hygienist
CESQG            Conditionally exempt small-quantity generator
Green-tip lamp   Lamps that may not be subject to universal waste rules
                 and have a TCLP value for mercury of less than 0.2 mg/L
NEMA             National Electric Manufacturers Association
OSHA             Occupational Safety and Health Administration
PEL              OSHA permissible exposure limit based on an 8-hour
                 time-weighted average
RCRA             Resource Conservation and Recovery Act
Silver-tip lamp  Lamps that exceed the maximum concentration of mercury
                 for the toxicity characteristic and are regulated as
                 hazardous or universal waste
SQG              Small-quantity generator of hazardous waste
SQHUW            Small-quantity handler of universal waste (generators
                 that handle less than 5,000 kg, in aggregate, of
                 universal waste per year)
TCLP             Toxicity characteristic leachate procedure
TLV              8-hour time-weighted exposure limits established by
                 ACGIH

TABLE 2 Results of Mercury Exposure Monitoring During Fluorescent-Lamp
Processing

                      Monitoring
Method                Type            Enclosed Setting
                                  Trial A            Trial B
                                  (mg/[m.sup.3])     (mg/[m.sup.3])

OSHA 140 (a)
                      Personal    0.05 (c)           0.05 (c)
                      Area        0.10 (c)           0.09 (c)
OSHA 145 (b)
                      Personal    1.4 x [10.sup.-4]  1.5 x [10.sup.-4]
                      Area        2.1 x [10.sup.-4]  1.9 x [10.sup.-4]
Jerome mercury meter
                      Personal    0.06 (c)           0.02
                      Area        0.10 (c)           0.03

                      Monitoring
Method                Type        Outdoor Setting
                                  Trial C            Trial D
                                  (mg/[m.sup.3])     (mg/[m.sup.3])

OSHA 140 (a)
                      Personal    0.03               0.02
                      Area        0.02               0.03
OSHA 145 (b)
                      Personal    1.6 x [10.sup.-4]  1.4 x [10.sup.-4]
                      Area        1.4 x [10.sup.-4]  1.7 x [10.sup.-4]
Jerome mercury meter
                      Personal    0.11 (c)           0.14 (c)
                      Area        0.08 (c)           0.04

                      Monitoring  t-Test Assessment of Aggregate
Method                Type        Difference Between Trial Locations

OSHA 140 (a)
                      Personal    p = .04 (d)
                      Area        p = .01 (d)
OSHA 145 (b)
                      Personal    p = .70
                      Area        p = .13
Jerome mercury meter
                      Personal    p = .08
                      Area        p = .94

(a) Expressed as an 8-hour time-weighted average, the OSHA Method 140
for mercury vapor in workplace atmospheres has a coefficient of
variation of 0.039.
(b) Expressed as an 8-hour time-weighted average, the OSHA Method 145
for particulate mercury in workplace atmospheres has a coefficient of
variation of 0.086.
(c) Exceeds OSHA permissible exposure limit of 0.05 mg/[m.sup.3].
(d) Statistically significant difference based on p value < .05.