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The concept of the exposure standard
Published in Sue Reed, Dino Pisaniello, Geza Benke, Kerrie Burton, Principles of Occupational Health & Hygiene, 2020
An ES can take one or all of three forms: Time-weighted average (TWA)—the average airborne concentration of a particular substance over a normal eight-hour working day, for a five-day working week. The TWA is the most common of the exposure standards and, except where a peak limitation has been assigned, virtually all substances are listed with a TWA.Short-term exposure limit (STEL)—a 15-minute TWA exposure which should not be exceeded at any time during a working day, even if the eight-hour TWA average is within the TWA ES. Exposures at the STEL should not be longer than 15 minutes and should not be repeated more than four times per day. There should be at least 60 minutes between successive exposures at the STEL.Peak—a maximum or peak airborne concentration of a particular substance determined over the shortest analytically practicable period that does not exceed 15 minutes.
Other Topics
Published in Jeff Kuo, Air Pollution Control Engineering for Environmental Engineers, 2018
Permissible exposure limits are established by OSHA and they are legal limits in the U.S. for exposure of an employee to a chemical substance or physical agent such as loud noise. A PEL is usually given as a time-weighted average (TWA). However, some are short-term exposure limits (STEL) or ceiling limits. A TWA is the average exposure over a specified period, usually a nominal eight hours. This implies that, for limited periods, a worker may be exposed to concentration excursions higher than the PEL, so long as the TWA is not exceeded. A STEL is one that addresses the average exposure over a 15-30 minute period of maximum exposure during a single work shift. A ceiling limit is one that may not be exceeded for any time, and is applied to irritants and other materials that have immediate effects.
Tables and Guidelines for Laboratory Safety
Published in Thomas J. Bruno, Paris D.N. Svoronos, CRC Handbook of Basic Tables for Chemical Analysis, 2020
Thomas J. Bruno, Paris D.N. Svoronos
STEL: Short-Term Exposure Level; an exposure limit for a short term; 15-minute exposure that cannot be exceeded during the workday, enforced by OSHA as a legal standard. Short-term exposures below the STEL level generally will not cause irritation, chronic or reversible tissue damage, or narcosis.
Establishment of Control Room Habitability Analysis Methodology Postulating the Event of Pressurized Tank/System of Hazardous Gas Release
Published in Nuclear Science and Engineering, 2023
Anjun Jiao, David Ricks, Thomas Remick, Brian J. Hansen
Figure 3 illustrates the control room R-134a transient concentration at the limiting break size of 0.126 in. The results of Case I illustrate that the control room R-134a concentration between 1000 PPM and 1114 PPM lasts less than 10 min. This well meets the STEL acceptance criterion for R-134a. The results of Case II indicate that the control room R-134a peak concentration is less than 600 PPM, which is much below the TWA acceptance limit of 1000 PPM. Thus, the control room habitability will not require a person to don a respirator, per the definitions of TWA and STEL. Note that (1) the definition of TWA is an 8-h shift average acceptable concentration and (2) the definition of STEL is the highest concentration of a chemical that a person can be exposed to for 15 min, twice per 8-h shift, without being required to don a respirator.
Evaluation of potential health effects associated with occupational and environmental exposure to styrene – an update
Published in Journal of Toxicology and Environmental Health, Part B, 2019
M.I. Banton, J.S. Bus, J.J. Collins, E. Delzell, H.-P. Gelbke, J.E. Kester, M.M. Moore, R. Waites, S.S. Sarang
The occupational ototoxicity data of Triebig, Bruckner, and Seeber (2009) indicate that the 8-h TWA OEL of 20 ppm styrene does not require any additional exposure notation such as a Short-Term Exposure Limit (STEL) designation. A STEL is an OEL notation designed to limit peak exposures when data indicate that short-term peak excursions during a workshift may induce rapid-onset toxicity (ACGIH, 2018). Triebig, Bruckner, and Seeber (2009) characterized styrene workplace exposures by extrapolation from end-of-shift urinary mandelic and phenylglyoxylic acid concentrations, and because biomonitoring captures only cumulative workshift exposures, such extrapolations reflect only TWA exposures. Thus, workers experiencing 30–50 ppm exposures identified as protective of ototoxicity could have still experienced workshift short-term exposure excursions regarded as complying with a TWA-only OEL. For example, ACGIH (2018) TLV® TWA-only values allow for transient exposure excursions that do not exceed 3 times the TWA for no more than 15 min at a time and 4 occasions during a workshift as long as the excursions are spaced at least 1 h apart. ACGIH guidance also indicates that no peak concentration should exceed fivefold the TWA. The ACGIH TWA criteria indicate that the non-ototoxic TWA exposures of 30–50 ppm styrene reported by Triebig, Bruckner, and Seeber (2009), therefore, could have contained short-term peak excursions reaching 90–150 ppm and still have been in compliance with an ACGIH TWA TLV®. Thus, the 20 ppm TWA-only OEL recommended for styrene is unlikely to present an adverse ototoxicity concern as long as repeated 15-min short-term excursions do not exceed 60 ppm, no excursion exceeds 100 ppm, and an 8-h TWA of 20 ppm is not exceeded. This conclusion is further supported by the observation that the only workers exhibiting possible mild ototoxicity in Triebig, Bruckner, and Seeber (2009) were long-term workers (mean job tenure of 15 years) who also experienced median TWA exposures of 80 ppm and greater prior to 1995. Using ACGIH guidance, an 80 ppm TWA exposure is greater than any 15 min excursion allowed for by a 20 ppm TWA, and 15 min excursions of 240 ppm styrene allowed for within an 80 ppm TWA are substantially higher than any maximum peak excursion of 100 ppm allowed for with a 20 ppm TWA.
A methodological approach for quantifying aerial formaldehyde released by some hair treatments-modeling a hair-salon environment
Published in Journal of the Air & Waste Management Association, 2021
Patrick Henault, Rémi Lemaire, Aurélie Salzedo, Joel Bover, Gérard Provot
Its toxicological profile, more related to inhalation than topical route, has been established by many official agencies (US EPA, ANSM France, Santé Canada], the exhaustive review of which has been performed by the World Health Organization (WHO), compiling 194 references (Kaden et al. 2010). With regard subjects prone to higher exposure conditions, through professional occupations, some official safety bureaus (NIOSH, National Institute for Occupational Safety and Health/US and AFSSET in France] recommended maximal limits of exposures to HCHO according to regular or short-term conditions as 1230 μg/m3 and 2460 μg/m3 (i.e. 1 and 2 ppm) respectively. The American Conference of Governmental Industrial Hygienists (ACGIH) in 2017 amended the HCHO exposure limits in workplaces as a result of the recent evolutions in the classification of this substance (https://catas.com/en-GB/news/acgih-sets-new-limits-for-exposure-to-formaldehyde-in-workplaces]. The Threshold Limit Values-TWA (time-weighted average) as per ACGIH is recommended at 0.1 ppm (corresponding to 123 μg/m3) which is the average concentration limit weighted throughout the working period (8 hours per day for 40 hours per week). The short-term exposure limit (STEL) which is the concentration limit for short exposures that shall be shorter than 15 min and only occasional is recommended at 0.3 ppm (corresponding to 370 μg/m3). A vast amount of toxicological data (based on animal models) converged to label HCHO as a dose-related potent toxic agent (acute toxicity, carcinogenicity, genotoxicity etc) that can seriously impact the human health at different levels (Bolt 1987; Bossetti et al. 2008; Harving et al. 1990; Krakowiak et al. 1998; Kriebel et al. 2001; Lang, Bruckner, and Triebig 2008; Paustenbach et al. 1997). These findings logically conveyed HCHO to being a highly regulated molecule in most countries. As an example, in EU the substance HCHO has a harmonized classification in Annex VI of Chemical Regulation (EC) No 1272/2008 (CLP Regulation) as Muta.2, H341/Carc.1B H350 and thus its use is banned in cosmetic products (article 15- EU Cosmetic Regulation N° 1223/2009/CE). In USA, HCHO is listed at the California’s Proposition 65 (Safe Drinking Water and Toxic Enf. Act, 1986) with a safe harbor level of 40 µg/day as carcinogenic.