National Academies Press: OpenBook

Options for Reducing Lead Emissions from Piston-Engine Aircraft (2021)

Chapter: Appendix E Occupational Health

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Page 124
Suggested Citation:"Appendix E Occupational Health." National Academies of Sciences, Engineering, and Medicine. 2021. Options for Reducing Lead Emissions from Piston-Engine Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26050.
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Page 124
Page 125
Suggested Citation:"Appendix E Occupational Health." National Academies of Sciences, Engineering, and Medicine. 2021. Options for Reducing Lead Emissions from Piston-Engine Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26050.
×
Page 125
Page 126
Suggested Citation:"Appendix E Occupational Health." National Academies of Sciences, Engineering, and Medicine. 2021. Options for Reducing Lead Emissions from Piston-Engine Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26050.
×
Page 126
Page 127
Suggested Citation:"Appendix E Occupational Health." National Academies of Sciences, Engineering, and Medicine. 2021. Options for Reducing Lead Emissions from Piston-Engine Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26050.
×
Page 127
Page 128
Suggested Citation:"Appendix E Occupational Health." National Academies of Sciences, Engineering, and Medicine. 2021. Options for Reducing Lead Emissions from Piston-Engine Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26050.
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Page 128

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PREPUBLICATION COPY – Uncorrected Proofs 124 Appendix E Occupational Health The U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA) has occupational exposure standards and related regulatory requirements designed to reduce health risks of workplace exposures to chemical contaminants to acceptable levels. The requirements are adopted, administered, and enforced by OSHA. There are 28 states and territories which operate their own occupational safety and health programs under a State Plan approved and monitored by OSHA. Twenty-two State Plans cover private-sector and state and local government workers; six State Plans cover state and local government workers only. State Plans adopt and enforce standards and investigate safety and health concerns in workplaces throughout the state. State Plans are required to have standards and enforcement programs that are at least as effective as those of OSHA but may have different or additional requirements.1 The OSHA standards apply to general aviation (GA) broadly and to occupational exposures to GA fuels and their combustion products. This discussion addresses three specific chemical compounds. These include inorganic lead (lead dibromide [PbBr2] [CAS# 10031-22- 8]) as an exhaust emission product of the combustion of leaded aviation gasoline) and the fuel additives tetraethyl lead (TEL) Pb(C2H5)4 (CAS# 78-00-02) and ethylene dibromide (EDB) (C2H4Br2) (CAS# 106-93-4).2 INDUSTRIAL HYGIENE AND OCCUPATIONAL HEALTH Table E-1 summarizes the current occupational exposure standards for lead exposure (inorganic lead and TEL) for the general industry as drawn from 29 CFR § 1910.1025 and Table Z-1 of 29 CFR § 1910.1000. Details on the industrial hygiene and occupational health control program requirements should be taken from the OSHA standards and requirements.3 The acronyms used are defined in the footnote below.4 Regarding the action level, under OSHA, the action level for any given air contaminant is generally set at one-half of the PEL, but the actual level may vary from exposure standard to exposure standard. The intent of the action level is to identify an 8- hour TWA exposure level, which, if achieved without respiratory protection, would indicate that the vast majority of randomly sampled exposures for the same employee group conducting the same workplace tasks will be below the PEL. 1 Personal communication, David Valiante, OSHA, June 17, 2020. 2 OSHA standards would apply to exposures to other organic compounds in GA fuels (e.g., benzene and toluene) but this is outside of the scope of this assessment. 3 Information on the requirements of the lead standard can be found at OSHA’s Lead Safety and Health Topic Page. OSHA regulations for organic lead such as TEL are in the form of PELs and can be found under OSHA’s air contaminants standard (29 CFR 1910.1000 and 29 CFR 1926.55). OSHA expanded health standard for lead, 1910.1025, specifically excludes organic lead (e.g., TEL). Overexposures under the lead standard apply only to inorganic lead (e.g., lead dibromide) and are assessed using both the action level and the PEL. See 29 CFR 1910.1025 for full detail. 4 OSHA PEL: permissible exposure level; TWA: time-weighted average.

PREPUBLICATION COPY – Uncorrected Proofs 125 TABLE E-1 Occupational Exposure Standards for Lead Exposure TEL PbBr2 as Lead (inorganic lead) OSHA & Cal OSHA PEL (8-hour TWA) 0.075 mg/m3 0.050 mg/m3 a OSHA action level (8-hour TWA) 0.5 of PEL 0.030 mg/m3 a The lead standard for general industry (29 CFR § 1910.1025) requires PEL adjustments with respect to extended work shifts (work shift longer than 8 hours). There are adjustments required for TEL in the OSHA regulations. Measured and confirmed workplace exposures below the action level generally require a report documenting the monitoring results (a negative initial determination) but no further action by the employer. For inorganic lead, the action level is 60 percent of the PEL, but, as is discussed below, the employer’s obligations to confirmed exposures above the action level are significant. The OSHA general industry standard for exposure to TEL (29 CFR § 1910.1000 and 29 CFR § 1926.55) and inorganic lead (29 CFR § 1910.1025) applies to GA aircraft operations and aircraft engine maintenance activities where exposure to lead and/or TEL are possible. To be more specific the provisions of 29 CFR § 1910.1025 do not apply to TEL because it is an organic lead compound. For inorganic lead (PbBr2), under 29 CFR § 1910.1025 (d)(2), through personal exposure monitoring, the employer is required to make an initial determination as to whether employee exposures exceed the action level value. This exposure monitoring can be conducted on all employees or on a representative sample of employees who would be expected to encounter the highest airborne concentrations of lead over an 8-hour work period. For workplaces with a larger number of exposed employees, another approach would be to monitor exposures for a smaller group of randomly selected employees with similar exposures. For many locations, it is expected that the number of exposed employees would be small, and this could lead to a decision to either monitor all employees or a smaller number of employees based on those with the largest expected lead exposures. It should be noted that the evaluation of the results of the personal exposure monitoring must also meet the accuracy requirements of 29 CFR § 1910.1025 (d)(9) and include a consideration of sampling and analysis error (SAE). This is necessary to account for occupational environment variations over the course of a work shift plus sampling and analytical errors. The analytical error is based on a standardized coefficient of variation for the analytical method used as provided by the National Institute for Occupational Safety and Health (NIOSH) while the occupational environment variations and sampling error are derived from the central tendency and spread of the sample distribution using data gathered from sampling exposures for randomly selected work days and randomly selected employees in the similar exposure group or an individual employee.5,6,7 Thus, when evaluating the exposure results, against the PEL or action level, the determination is based on the value of the average exposure estimate relative to the 95 percent confidence levels for the data and the other SAE inputs. 5 OSHA Technical Manual (OTM), OSHA Instruction TED 01-00-015 [TED 1-0.15A], Section II, chapter 1. Available at: https://www.osha.gov/dts/osta/otm/otm_ii/otm_ii_1.html#receive_sample_results. 6 For lead sampling and analytical information, see Lead by Flame AAS. In: NIOSH Manual of Analytical Methods (NMAM), Fifth Edition. Available at: https://www.cdc.gov/niosh/docs/2014-151/pdfs/methods/7082.pdf. 7 NIOSH (1977).

PREPUBLICATION COPY – Uncorrected Proofs 126 Furthermore, regarding inorganic lead assessments, if the action level is exceeded, then the regulation prescribes that the employer conduct exposure monitoring for all exposed employees. The results of this monitoring are reported to all affected employees. If the PEL is exceeded, the employer is then required to implement engineering, work practice, administrative controls, and perhaps to supply various forms of personal protective equipment (PPE) to reduce levels air concentrations below the PEL and reduce skin and eye absorption. Beyond this, there are several work area housekeeping and hygiene facilities and practices requirements designed to eliminate the accumulation of inorganic lead dust or the re-entrainment of this lead dust, the inadvertent ingestion or absorption of this lead dust, or its transport outside of the work area. In addition, there are explicit and detailed medical surveillance and biological monitoring requirements for employees exposed above the action level for more than 30 days per year, including specific requirements related to measurement of blood lead level (BLL) expressed in ug/deciliter. Also, there are explicit training requirements for any employee exposed to lead, as well as hazard communication requirements under the OSHA Hazard Communication Standard (29 CFR § 1910.1200) for lead. The situation is less complex for exposures to TEL. There are no explicit requirements beyond establishing statistically (as described above for inorganic lead) that the average exposure estimate does not exceed the PEL or action level. In this case, the exposure determination may be either qualitative or quantitative. If exposures are above the action level, then it must be established statistically through additional sampling that they do not exceed the PEL. If exposures do exceed the PEL, then controls (engineering, work practice, PPE, administrative) are needed to reduce exposures. The OSHA standard does not explicitly call for personal exposure monitoring for TEL, so an analysis based on exposure measurements for similar workplaces and similar tasks, engineering evaluation, or worst-case exposure calculations may be a path for the required initial determination. A review of the chemical and physical characteristics of the material, quantity of use, frequency of use, conditions under which it is used and experience with similar operations may be sufficient to characterize exposures to a workplace hazard. Either way, the basis for this determination must be documented and the records retained. The compliance determinations for inorganic lead and TEL may be complicated for airport workers exposed to both lead dibromide and TEL. In this case, OSHA standard 29 CFR § 19.1000 (d)(2)(i) treats this as a mixture and evaluates this as “combined” exposure because the effects could be additive: [(8-hr TWA TEL exposure/0.075 mg/m3) + (8-hr TWA Pb exposure/0.05 mg/m3)]. Under the OSHA technical manual, the SAE (95 percent confidence) of the substances comprising the mixture can be pooled to give the SAE of the mixture and the determination rules described in the manual can then be applied to the mixture relative to unity as opposed to the PEL.8 The concept of action level does not apply to the mixture, only the individual contaminants. 8 OSHA Technical Manual, OSHA Instruction TED 01-00-015 [TED 1-0.15A], Section IV D. 4. SAEs for Exposures to Chemical Mixtures. Available at: https://www.osha.gov/dts/osta/otm/otm_ii/otm_ii_1.html#receive_sample_results.

PREPUBLICATION COPY – Uncorrected Proofs 127 One final point regarding exposure to Grade 100 and 100LL vapor involves EDB. As was mentioned above, EDB is a fuel additive which performs the role of a lead scavenger in the exhaust gas. However, it also exists as a vapor in fuel tanks and is released to the atmosphere during refueling and while aircraft are parked. Its potential exposure routes include inhalation, absorption, ingestion, and contact. The PEL, ceiling and peak exposure standards and the action level from Table Z-2 of 29 CFR § 1910.1000 are presented in Table E-2; reference to OSHA standards and requirements of 29 CFR § 1910.1000 and § 1926.55 is recommended. TABLE E-2 Ethylene Dibromide OSHA Exposure Standards EDB OSHA PEL (8-hour TWA)/C/P 20 ppm/30 ppm any time/50 ppm-5 minute maximum peak OSHA action level (8-hour TWA) 0.5 of PEL Several times in this discussion mention has been made that TEL and EDB are an absorption hazard through dermal, mucous membranes, and eyes. Both compounds carry a skin hazard designation in the OSHA standard and evaluations of these three routes of exposure should be included in any industrial hygiene assessments for these workplaces. FBOS, REPAIR AND OVERHAUL SHOPS, AND AIRPORTS The purpose of the discussion above was to provide background for understanding occupational health requirements for exposures to leaded aviation gasoline and its combustion products. Specifically, there is the need for assessment of TEL, lead bromide, and EDB exposures in airport workplaces such as flight line operations and in those repair and overhaul shops where GA aircraft and engines using aviation gasoline are maintained.9 It seems evident that exposures to lead are common for flight line and maintenance shop workers at airports with GA aircraft including those employed by the airport itself, fixed base operators (FBOs), and repair/overhaul facilities. This would include exposure to inorganic lead (lead bromide) because of the combustion of leaded aviation gasoline in aircraft engines and TEL and EDB as a result of refueling aircraft and maintenance activities. Even incidental exposures to employees not directly engaged in these work functions are also possible and these employees must be included in industrial hygiene assessments. For TEL and EDB, there may be direct exposures as a result of activities such as the handling of engine parts wetted with leaded aviation gasoline by mechanics, the dispensing and inadvertent spillage of aviation gasoline by aircraft ground service operators, or the improper use of aviation gasoline as a shop solvent for parts cleaning, or perhaps other purposes. These TEL and EDB exposures may involve inhalation, ingestion, and absorption. Due to its vapor pressure at 25°C (0.23 psi) and its concentration in the liquid (based on a 1:1 molar ratio dosing rate for TEL and EDB), inhalation exposures to EDB are possible, especially during refueling. To some 9 For an example of a comprehensive airport lead workplace exposure and program assessment see Chen and Eisenberg (2013).

PREPUBLICATION COPY – Uncorrected Proofs 128 degree TEL and EDB contained in aviation gasoline vapor may be transported downstream of the location of the refueling event. Lead bromide presents a different exposure picture. Lead bromide is a product of engine exhaust and could originate anywhere the aircraft engine is operating including maintenance and repair facilities and operational areas on the airport grounds. Aircraft lead dibromide emissions are transported downwind from the aircraft location. The concentrations vary with downwind distance and the local concentrations can vary with meteorology, terrain, and local factors. With the large number of airports and the widespread use of leaded aviation gasoline, lead dibromide is expected to be commonly found in many airport workplaces or as an incidental exposure to those working nearby. As discussed above, there are different PELs for exposures to inorganic lead, TEL, and EDB and separate exposure assessments and compliance actions are required under OSHA regulations. At a minimum, an initial exposure determination is needed for each employee or group of similarly exposed employees in the workplace for each air contaminant found in the workplace. If the determination is that the exposure is below the action level, then a negative initial determination must be documented. If the initial assessment indicates that the exposure is above the action level, this must also be documented and either more personal exposure monitoring may be required to determine compliance and perhaps workplace controls. As discussed in (29 CFR 1910.1025), there are very specific additional requirements for inorganic lead exposures above the action level. REFERENCES Chen, L., and J. Eisenberg. 2013. Health hazard evaluation program: Exposures to lead and other metals at an aircraft repair and flight school facility. NIOSH Report No. 2012-0115- 3186. Cincinnati, OH, U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Available at: http://www.cdc.gov/niosh/hhe/reports/pdfs/2012-0115-3186.pdf. NIOSH (National Institute for Occupational Safety and Health). 1977. Occupational Exposure Sampling Strategy Manual. Publication No. 77-173. January. Available at: https://www.cdc.gov/niosh/docs/77-173/default.html.

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Small gasoline-powered aircraft are the single largest emitter of lead in the United States, as other major emission sources such as automobile gasoline have been previously addressed. A highly toxic substance that can result in an array of negative health effects in humans, lead is added to aviation gasoline to meet the performance and safety requirements of a sizable portion of the country’s gasoline-powered aircraft.

Significantly reducing lead emissions from gasoline-powered aircraft will require the leadership and strategic guidance of the Federal Aviation Administration (FAA) and a broad-based and sustained commitment by other government agencies and the nation’s pilots, airport managers, aviation fuel and service suppliers, and aircraft manufacturers, according to a congressionally mandated report from the National Academies of Sciences, Engineering, and Medicine.

While efforts are underway to develop an unleaded aviation fuel that can be used by the entire gasoline-powered fleet, the uncertainty of success means that other steps should also be taken to begin reducing lead emissions and exposures, notes the report, titled TRB Special Report 336: Options for Reducing Lead Emissions from Piston-Engine Aircraft.

Piston-engine aircraft are critical to performing general aviation (GA) functions like aerial observation, medical airlift, pilot training, and business transport. Other GA functions, such as crop dusting, aerial firefighting, search and rescue, and air taxi service, have particular significance to communities in rural and remote locations.

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