Flavorings-Related Lung Disease: Occupational Exposure Limits
Occupational Exposure Limits
Occupational exposure limits are developed by federal agencies and safety and health organizations to prevent adverse health effects from workplace exposures.
Occupational Safety and Health Administration (OSHA) [Mandatory]
- The U.S. Department of Labor’s OSHA permissible exposure limits (PELs) are legal limits enforceable in workplaces covered under the Occupational Safety and Health Act.
- OSHA PELs represent the legal maximum for a time-weighted average (TWA) exposure to a physical or chemical agent over a work shift [OSHA 2018].
- OSHA short-term exposure limits (STELs) are the legal maximum average exposure for a 15-minute time period.
- Some chemicals also have an OSHA ceiling value that represent levels that must not be exceeded at any time.
- For substances for which an OSHA PEL has not been issued, violation of the OSHA General Duty Clause can be considered using available occupational exposure references and recommendations [OSHA 1993; OSHA 2003], such as the American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Values (TLVs®) and NIOSH.
American Conference of Governmental Industrial Hygienists (ACGIH®) [Recommendations]
- ACGIH® is a professional, not-for-profit scientific association that reviews existing published, peer-reviewed scientific literature and publishes recommendations for safe levels of substances in air based on an 8-hour workday and 40-hour workweek. These recommendations are called TLVs® [ACGIH 2018].
- ACGIH TLVs are not standards; they are health-based guidelines derived from scientific and toxicological information.
- ACGIH provides TLV®-TWA guidelines that are levels that should not be exceeded during any 8-hour workday of a 40- hour workweek.
- ACGIH also provides TLV®-STEL guidelines which are 15-minute exposure levels that should not be exceeded during a workday.
- Exposures above the TLV®-TWA but less than the TLV®-STEL should be (1) less than 15 minutes, (2) occur no more than four times a day, and (3) be at least 60 minutes between exposures [ACGIH 2018].
- Additionally, ACGIH provides TLV®-Ceiling values which are levels that should not be exceeded at any time during a work shift.
National Institute for Occupational Safety and Health (NIOSH) [Recommendations]
- NIOSH provides TWA concentrations that should not be exceeded over an 8 or 10-hour work shift, during a 40-hour workweek [NIOSH 2010].
- RELs are intended to be protective over a 45-year working lifetime.
- NIOSH also provides STELs which are 15-minute TWA exposures that should not be exceeded at any time during a workday [NIOSH 2010].
- Some chemicals have ceiling values which are concentrations that should not be exceeded at any time [NIOSH 2010].
- For some chemicals, NIOSH has Immediately Dangerous to Life or Health (IDLH) values. An IDLH value is a concentration of an air contaminant that can cause death or immediate or delayed permanent adverse health effects, or prevent escape from such an environment.
Occupational exposure limits for dust, carbon monoxide, carbon dioxide, diacetyl, and 2,3-pentanedione are listed in the Table 1.
- There are no exposure guidelines specific for coffee dust.
- OSHA has a PEL for airborne total dust not to exceed 15 mg per cubic meter (mg/m3) over an 8-hour TWA limit for workplace exposures to total dust. Total dust means particles of various sizes; some may be too big to enter the deepest areas of the lungs but can enter the nose, mouth, and upper airways during breathing. Total dust particles can come from natural forces or made-made processes. Total dust can consist of minerals, metals, chemicals, and biological or organic compounds.
- OSHA has a PEL for respiratory dust not to exceed 5.0 mg/m3 over an 8-hour TWA limit for workplace exposures to respirable dust. Respirable dust is made up of particles that reach the deepest areas of the lungs.
- ACGIH has guidelines that recommend airborne concentrations of respirable dust be kept below 3 mg/m3.
- ACGIH has guidelines that recommend airborne concentrations of inhalable dust be kept below 10 mg/m3. Inhalable dust a term that means particles of various sizes. Some of the particles may be too large to enter the deepest areas of the lungs but can enter the nose, mouth, and upper airways during breathing. Inhalable dust is collected using a different method than total dust.
- NIOSH has a REL for carbon monoxide not to exceed 35 parts per million (ppm) over an 8-hour TWA and 200 ppm as an absolute ceiling.
- NIOSH also has an IDLH air concentration of 1,200 ppm for carbon monoxide that can cause death or immediate or delayed permanent adverse health effects, or prevent escape from such an environment.
- ACGIH (25 ppm) and OSHA (50 ppm) have 8-hour TWA limits for workplace exposures to carbon monoxide.
- NIOSH, ACGIH, and OSHA limits are designed for occupational exposure measurements in manufacturing and other trades that have potential sources of carbon monoxide. Typical levels of carbon monoxide in offices are 0 to 5 ppm [Illinois Department of Public Health 2018].
- NIOSH has a REL for carbon dioxide not to exceed 5,000 ppm over an 8-hour TWA and a 15-minute TWA STEL of 30,000 ppm for carbon dioxide in workplace air.
- NIOSH also has an IDLH air concentration of 40,000 ppm that can cause death or immediate or delayed permanent adverse health effects, or prevent escape from such an environment.
- ACGIH has an 8-hour TLV-TWA of 5,000 ppm and a 15-minute TWA STEL of 30,000 ppm for workplace exposures to carbon dioxide.
- OSHA has an 8-hour TWA PEL of 5,000 ppm for carbon dioxide.
- NIOSH, ACGIH, and OSHA limits are designed for occupational exposure measurements in manufacturing and other trades that have potential sources of carbon dioxide (e.g., welding, vehicle exhaust, diesel engine exhaust, or coffee roasting).
- In office settings, carbon dioxide generally should not be greater than 700 ppm above outdoor carbon dioxide levels; this typically corresponds to indoor concentrations below 1,200 ppm [ANSI/ASHRAE 2016].
Diacetyl and 2,3-Pentanedione
The NIOSH RELs for occupational exposures to diacetyl and 2,3-pentanedione are intended to reduce the risk of respiratory impairment (decreased lung function) and the irreversible (permanent) lung disease, obliterative bronchiolitis.
- NIOSH has 8-hour TWA RELs for diacetyl (5 parts per billion [ppb]) and 2,3-pentanedione (9.3 ppb) in workplace air.
- NIOSH has 15-minute TWA STELs for diacetyl (25 ppb) and 2,3-pentanedione (31 ppb).
- ACGIH has an 8-hour TWA TLV (10 ppb) and a 15-minute TWA STEL (20 ppb) for workplace exposures to diacetyl.
- OSHA has no PELs for diacetyl or 2,3-pentanedione.
Task-based Exposures to Diacetyl and 2,3-Pentanedione
The establishment of a STEL is based on the concern that peak exposures may have greater toxicity than the same total dose spread out over a longer period. Air sampling during specific tasks, such as roasting, grinding, packaging, opening storage bins or containers with roasted coffee beans, and pouring and adding flavorings, is an important way to identify where peak exposures may occur and for targeting workplace interventions (e.g., engineering controls, ventilation changes) to reduce contaminant air concentrations.
- Roasting, grinding, flavoring, and packaging roasted coffee are sources of diacetyl and 2,3-pentanedione exposure.
- NIOSH has sampled these tasks, with varying durations with some only lasting a few seconds or minutes (e.g., grinding, packaging), to understand which tasks may contribute to higher exposures to diacetyl and 2,3-pentanedione.
- Exposures to diacetyl and 2,3-pentanedione during grinding and flavoring are those most likely to exceed the NIOSH RELs.
- Increases in production volume, modifications to work practices, or changes in ventilation could result in worker exposures above the RELs and STELs for diacetyl or 2,3-pentanedione.
Diacetyl Exposure and Effects on Lung Function
Findings from studies of workers engaged in microwave popcorn and flavorings production were used by NIOSH to estimate worker risks for occupational lung disease by means of mathematical models of diacetyl exposure and indicators of potential occupational disease. In particular, NIOSH related multiple endpoints used to describe pulmonary impairment to levels of diacetyl exposure. Most of these endpoints are thought to occur early in the progression of more severe respiratory impairment. Table 2 shows different endpoints from a study of microwave popcorn workers. In evaluating the data, NIOSH concluded that the risk from exposure to an average airborne concentration of 5 ppb diacetyl over a 45-year working lifetime is about 1 to 2 excess cases of respiratory impairment per 1000 workers.
- NIOSH measured lung function in microwave popcorn and flavorings production workers using a breathing test called spirometry. This test measures a person’s ability to move air out of their lungs. A person taking this breathing test places a padded nose clip on his or her nose, then breathes in as deeply as possible, and forcefully blows out as quickly and completely as possible through a tube attached to a spirometer machine.
- The test includes many measurements or calculations including the following three: 1) forced expiratory volume in one second (FEV1) – the amount of air that the participant can blow out in the first second of exhaling, 2) forced vital capacity (FVC) – the total amount of air the participant can forcefully blow out after taking a deep breath), and 3) the ratio of FEV1 to FVC (FEV1/FVC).
- Spirometry test results are compared to expected normal values [Hankinson et al. 1999]. For spirometry, the normal range is defined as the range of values which encompasses 95% of a healthy, non-smoking population (classified by age, gender, race and height). The lower limit of normal (LLN) is the cut-off below which results from only 5% of healthy individuals will fall. In other words, the lower limit of normal is defined as that value which identifies the lower 5th percentile of a healthy population of non-smokers (classified by age, gender, race, and height).
- The American Thoracic Society describes the severity of a spirometric abnormality based on a person’s percent of predicted FEV1. For example, a reduction in FEV1 below 60% of predicted (substantially less than the LLN) describes at least moderately severe impairment [Pellegrino et al. 2005].
Table 2 shows that, within the range of these models, based on FEV1 and the FEV1/FVC ratio, about 1-2 workers out of 1000 exposed to 5 ppb diacetyl over a 45-year working lifetime are estimated to develop spirometric evidence of exposure-related respiratory impairment. At 1 ppb, the risk is reduced to 2-4 in 10,000 workers (0.2-0.4 per 1000), and at 10 ppb, the risk increases to about 2-4 workers in 1000. When considering more severe lung disease (defined as at least moderately severe by the American Thoracic Society based on FEV1 below 60% predicted), NIOSH predicted that at 10 ppb as a TWA over a full shift for a 45-year working lifetime, 2 in 10,000 workers (0.2 in a 1000 workers) would suffer this level of impairment; at 5 ppb, about 1 in 10,000 workers (0.1 in a 1000 workers) would suffer this level of impairment.
These estimates depend on several assumptions and limitations in data; therefore, the risks shown are imprecise. When using inexact estimates in making exposure recommendations, NIOSH chooses methods that generally favor protection of workers. Given there is residual risk at the REL, NIOSH recommends that exposures to diacetyl be kept below the REL of 5 ppb and as low as practical. Risk is best managed using a comprehensive safety and health program that includes engineering controls, exposure monitoring, routine medical surveillance, and employee training in good work practices.