The Occupational Alliance for Risk Science (OARS) is an initiative to facilitate sharing of information with workers and occupational health and safety professionals. OARS provides a forum for information exchange about exposure guidance for chemical stressors, methods for improving occupational risk assessments, and training opportunities. The OARS serves as the home of exposure guide values, and related guideline documents, for chemical stressors. These guide values and supporting documentation related to worker and community exposure levels for chemical and physical agents and stressors are published by the OARS. OARS is managed by Toxicology Excellence for Risk Assessment (TERA).
![]() |
---|
• January 2025: OARS WEEL documentation for Methyltrimethoxysilane (MTMS) was published online in Toxicology and Industrial Health. Available at: https://journals.sagepub.com/doi/full/10.1177/07482337241301523
• January 2025: OARS WEEL documentation for (E)-1,1,1,2,2,5,5,6,6,6-Decafluoro-3-hexene (HFO-153-10mczz-E) was published online in Toxicology and In• November 2024: OARS WEEL documentation for Vinyltrimethoxysilane (VTMS) as been submitted to Toxicology and Industrial Health for publication.
• November 2024: OARS WEEL documentation for Vinyltrimethoxysilane (VTMS) as been submitted to Toxicology and Industrial Health for publication.
• June 2024: OARS WEEL documentation for Bis-(2-Chloroisopropyl) Ether (BCIPE) was published online in Toxicology and Industrial Health. Available at: https://journals.sagepub.com/doi/10.1177/07482337241245745. For questions, please contact Dr. Patricia McGinnis at mcginnis@tera.org.
• June 2024: OARS WEEL documentation for HFO-153-10mczz-E has been submitted to Toxicology and Industrial Health for publication.
• June 2024: OARS WEEL documentation for Methyltrimethoxysilane (MTMS) has been submitted to Toxicology and Industrial Health for publication.
![]() |
---|
The OARS-WEEL Committee consists of volunteer experts dedicated to the science of setting occupational exposure levels. The Committee strives for a balance of toxicology and industrial hygiene professionals with a broad base of experience from industry, government, academia, and consulting services. Each member serves on the Committee solely in his/her individual capacity and not as a representative of his/her employer, organization and/or agency.
![]() |
---|
The development of new or revision of existing WEELs is typically assigned to voluntarily designated subcommittees. A subcommittee usually comprises 3 – 4 members from the WEEL Committee. New WEELs are developed using the OARS-WEEL administrative standard operating procedure (SOP), while existing WEELs are usually revised every 10 years, unless the availability of significant new data which may impact the existing WEEL value compels the committee to make a revision sooner. The OARS-WEEL SOP contains procedures and guidelines governing conflicts of interest, draft document preparation, literature searches, draft document review, balloting process, post-ballot WEEL documentation quality assurance scientific review, and publication.
Once a subcommittee has prepared a draft WEEL document, a review of the draft is scheduled for the next available Committee meeting. The WEEL Committee members are expected to have reviewed all such drafts prior to the meeting. If no major changes are necessary to a draft, the attending Committee membership may, by a simple majority, approve the WEEL for balloting. Alternatively, the Committee may direct the subcommittee to revise the WEEL and present it for further discussion at a future meeting. If a ballot is not approved by a two-thirds majority of non-abstaining Committee members, it is discussed at the next Committee meeting to determine the appropriate course of action. Once the WEEL is approved by a two-thirds majority of non-abstaining Committee members, copies of ballot comments are forwarded to the designated subcommittee and all substantive comments must be addressed in the final draft. If resolution of a substantive comment results in a change to the WEEL value or a change in the basis for the value, the draft must be re-balloted.
Once all comments have been addressed on a successfully balloted draft, document formatting and editorial review are performed by TERA, before the draft WEEL document is made available for public comment (usually for a period of 30 days but may be extended if the need arises). After the public comment period has elapsed, comments are addressed by the subcommittee responsible for that specific draft, after which the WEEL documentation is submitted to Toxicology and Industrial Health (TIH), a peer-reviewed medical journal that covers research in the fields of occupational health and toxicology, for publication. A thorough review of the galley proof by the scientific content quality coordinator at TERA, and proofreaders and editors at TIH is the penultimate step before eventual publication of the WEEL documentation.
![]() |
---|
Occupational exposure limits (OELs) are developed for protection of healthy workers; they are not intended for the general public, which includes sensitive populations such as infants, the elderly, or the infirm. OELs are based on repeated daily exposures over a working lifetime. They are normally averaged over an 8-hour workday and serve to protect against acute and chronic health effects.
![]() |
Workplace Environmental Exposure Levels (WEELs) are health-based guide values for chemical stressors. The WEELs provide air concentrations intended to protect most workers from adverse health effects related to occupational chemical exposures. |
---|
![]() |
---|
Click Here to download the PDF version of the table
Substance | CAS | Source | 8-Hour TWA | Ceiling or Short- Term TWA |
Last Revised |
Acetone Cyanohydrin | 75-86-5 | AIHA | 2 ppm (skin) | 5 ppm (15 min, skin) | 1992 |
Acetophenone | 98-86-2 | AIHA | 10 ppm | 2007 | |
Aldicarb | 116-06-3 | AIHA | 0.01 mg/m3 (skin) | — | 2009 |
Allyl lsothiocyanate | 57-06-7 | AIHA | — | 1 ppm (15-min, skin, DSEN) |
1993 |
Aminobenzoic Acid, para- | 150-13-0 | AIHA | 5 mg/m3 | 2001 | |
Aminotri (Methylenephosphonic Acid) | 6419-19-8 | AIHA | 10 mg/m3 | 2004 | |
Amyl Alcohol, n- | 71-41-0 | AIHA | 100 ppm | 2001 | |
Benzaldehyde | 100-52-7 | AIHA | 2 ppm | 4 ppm (15-min, DSEN) |
1998 |
Benzenesulfonicacid, 5-chloro-2((2-Hydroxy-1 napthalenyl)-azo)-4-methyl, barium salt (2:1) |
5160-02-1 | AIHA | 1 mg/m3 | 2008 | |
Benzophenone | 119-61-9 | AIHA | 0.5 mg/m3 | 2003 | |
Benzoyl Chloride | 98-88-4 | AIHA | — | 5 ppm (ceiling, skin, DSEN) |
2008 |
Benzyl Alcohol | 100-51-6 | AIHA | 10 ppm | 2008 | |
Butylcatechol, 4-tert- | 98-29-3 | AIHA | — | 2 mg/m3 (ceiling, skin, DSEN) |
2001 |
Butyraldehyde | 123-72-8 | OARS | 25 ppm (75 mg/m3) | — | 2016 |
Chloramphenicol | 56-75-7 | AIHA | 0.5 mg/m3 | 2008 | |
ChIoroisopropyI)Ether, bis-(2- | 39638-92-9 | AIHA | 3 ppm | 2009 | |
Chloropropane, 2- | 75-29-6 | OARS | 50 ppm (161 mg/m3) | — | 2016 |
Chlorosulfonic Acid | 7790-94-5 | OARS | 2016* | ||
Chlorotrifluoroethylene | 79-38-9 | AIHA | 5 ppm | 2010 | |
Cumene Hydroperoxide | 80-15-9 | AIHA | 1 ppm (skin) | — | 2009 |
Decabromodiphenyl Oxide | 1163-19-5 | AIHA | 5 mg/m3 | 2009 | |
Decafluoropentane, 1,1,1,2,3,4,4,5,5,5- (HFC- 4310mee) | 138495-42-8 | OARS | 225 ppm (2320 mg/m3) | 700 ppm (7217 mg/m3) |
2020 |
Decafluoro-3-hexene, (E)- 1,1,1,2,2,5,5,6,6,6- (HFO-153-10mczz-E) | 1256353-26-0 | OARS | 200 ppm (2160 mg/m3) | 2024 | |
Decamethylcyclopentasiloxane (D5) | 541-02-6 | OARS | 10 ppm | 2015 | |
Decene, 1- | 872-05-9 | AIHA | 100 ppm | — | 2000 |
Dehydrolinalool | 29171-20-8 | AIHA | 2 ppm | — | 2007 |
Diallylamine | 124-02-7 | AIHA | 1 ppm (skin) | 2009 | |
Dibromoneopentyl Glycol | 3296-90-0 | AIHA | 0.2 mg/m3 | 2010 | |
Dibutylamine | 111-92-2 | AIHA | 5 ppm (ceiling, skin) | 2003 | |
Dichlorophenol, 2,4- | 120-83-2 | AIHA | 1 ppm (skin*) | — | 2004 |
Diethylbenzenes, mixed isomers | 25340-17-4 | AIHA | 5 ppm | 2005 | |
Diethylene Glycol | 111-46-6 | OARS | 10 mg/m3 | 2016 | |
Diethylene Glycol Monoethyl Ether | 111-90-0 | AIHA | 25 ppm | 1991 | |
Difluoroethane, 1,1- | 75-37-6 | AIHA | 1000 ppm | 2005 | |
Difluoroethane, 1-ChIoro-1,1- | 75-68-3 | AIHA | 1000 ppm | — | 1994 |
Difluoroethylene, (E)-1,2 (HFO-1132 (E) | 1630-78-0 | OARS | 350 ppm | 2022 | |
Difluoromethane | 75-10-5 | AIHA | 1000 ppm | 1997 | |
Diisobutylene | 25167-70-8 | OARS | 75 ppm (344 mg/m3 ) | 2016 | |
Dimethyl Ether | 115-10-6 | OARS | 1000 ppm | 2022 | |
Dimethyl Sulfoxide | 67-68-5 | AIHA | 250 ppm | — | 2003 |
Dimethyl Terephthalate | 120-61-6 | AIHA | 5 mg/m3 (total) | — | 2000 |
Dimethyldichlorosilane | 75-78-5 | AIHA | 2 ppm (ceiling) | 2001 | |
Dimethylethylamine | 598-56-1 | AIHA | 1 ppm | 3 ppm | 2011 |
Dimethyl-para-toluidine, n,n- | 99-97-8 | AIHA | 0.5 ppm | 2009 | |
Dinitroanisole, 2,4- (DNAN) | 119-27-7 | OARS | 0.1 mg/m3 (0.01 ppm) | 2014 | |
Dowtherm Q | 612-00-0, 68987-42-8 |
AIHA | 7.8 mg/m3 | 2002 | |
Epoxybutane, 1,2- | 106-88-7 | AIHA | 2 ppm | 2003 | |
Erythromycin | 114-07-8 | AIHA | 3 mg/m3 | 2007 | |
Fluoroethane, 1,1-dichloro-1- | 1717-00-6 | AIHA | 500 ppm | 3000 ppm (5-min STEL) |
2008 |
Furan | 110-00-9 | AIHA | Worker exposure by all routes should be minimalized to the fullest extent possible. |
1993 | |
GlycidylMethacrylate | 106-91-2 | AIHA | 0.5 ppm (skin, DSEN) | — | 2000 |
Glyoxal | 107-22-2 | AIHA | 0.1 mg/m3 (DSEN) | 2000 | |
Hexadiene, 1,4- (mixed cis and trans) | 592-45-0 | AIHA | 10 ppm | — | 2009 |
Hexafluoro-2-butene, cis-1,1,1,4,4,4- (HFO 1336mzz-Z) |
692-49-9 | OARS | 500 ppm (3350 mg/m3) | — | 2014 |
Hexafluoro-2-butene, trans-1,1,1,4,4,4- (HFO 1336mzz-E) |
66711-86-2 | OARS | 400 ppm (2680 mg/m3) | — | 2018 |
Hexafluoropropane, 1,1,1,3,3,3- | 690-39-1 | AIHA | 1000 ppm | 1998 | |
Hexamethyldisilazane (HMDZ) | 999-97-3 | OARS | 10 ppm | 50 ppm | 2018 |
Hexamethylene Glycol | 629-11-8 | AIHA | 10 mg/m3 | 2011 | |
Hexanediamine, 1,6- | 124-09-4 | AIHA | 1 ppm | 2004 | |
Hexanediol Diacrylate | 13048-33-4 | AIHA | 1 mg/m3 (DSEN) | 1998 | |
Hexyl Alcohol, n- | 111-27-3 | AIHA | 40 ppm (eye irritation) | 2011 | |
HFE-7100 | 163702-07-6, 163702-08-7 |
AIHA | 750 ppm | 1999 | |
Hydroxybenzoic Acid, 4- | 99-96-7 | OARS | 5 mg/m3 | 2016 | |
Isobutyraldehyde | 78-84-2 | AIHA | 25 ppm | — | 2002 |
Isocyanuric Acid | 108-80-5 | AIHA | 10 mg/m3 (total); 5 mg/m3 (respirable) |
2005 | |
Isophthalic Acid | 121-91-5 | AIHA | 10 mg/m3 (total); 5 mg/m3 (respirable) |
1991 | |
Isoprene | 78-79-5 | AIHA | 2 ppm | 2004 | |
Limonene, d- | 5989-27-5 | AIHA | 30 ppm | 1993 | |
Lithium Hydroxide | 1310-65-2 | AIHA | 1 mg/m3 (ceiling) | 1999 | |
Lithium Oxide | 12057-24-8 | AIHA | 1 mg/m3 (ceiling) | 1999 | |
Mancozeb | 8018-01-7 | AIHA | 1 mg/m3 (total, DSEN) | 2008 | |
Melamine | 108-78-1 | OARS | 3 mg/m3 | 2016 | |
Menthol | 1490-04-6 | OARS | 1 ppm | 3 ppm (15 min) | 2014 |
Mercaptobenzothiazole, 2- | 149-30-4 | AIHA | 5 mg/m3 (skin, DSEN) | 2010 | |
Mercaptoethanol | 60-24-2 | AIHA | 0.2 ppm (skin) | 2002 | |
Methoxypropylamine, 3- | 5332-73-0 | AIHA | 5 ppm | 15 ppm (15 min) | 2009 |
Methoxytridecafluoroheptene isomers (MPHE) | Variable | OARS | 200 ppm | — | 2020 |
Methyl Ethyl Ketoxime | 96-29-7 | AIHA | 10 ppm (DSEN) | 1990 | |
Methyl-2-PyrroIidone, n- (NMP) | 872-50-4 | OARS | 15 ppm (60 mg/m3) Skin | 30 ppm (120 mg/m3) | 2021 |
Methyltrichlorosilane | 75-79-6 | AIHA | 1 ppm (ceiling) | 2001 | |
Monochloroacetic Acid | 79-11-8 | AIHA | 0.5 ppm (skin) | 2004 | |
Nitro-1,2,4-TriazoI-5-One, 3- (NTO) | 932-64-9 | OARS | 2 mg/m3 | 2014 | |
Nitroguanidine, 1- (NQ) | 556-88-7 | OARS | 7 mg/m3 | — | 2016 |
Octamethylcyclotetrasiloxane (D4) | 556-67-2 | OARS | 10 ppm | 2014 | |
Octanol, 1- | 111-87-5 | AIHA | 50 ppm | 2005 | |
Octene, 1- | 111-66-0 | AIHA | 75 ppm | 2000 | |
Pentaerythritol Triacrylate | 3524-68-3 | AIHA | 1 mg/m3 (DSEN) | — | 1999 |
Pentafluoroethane, 1,1,1,2,2- | 354-33-6 | AIHA | 1000 ppm | 2009 | |
Pentafluoropropane, 1,1,1,3,3- | 460-73-1 | AIHA | 300 ppm | 2001 | |
Phosphono-1,2,4 butanetricarboxylic, 2-acid | 37971-36-1 | AIHA | 10 mg/m3 | 2006 | |
Picolines | 109-06-8, 108- 99-6, 108-89-4 |
AIHA | 2 ppm (skin) | 5 ppm (15-min, skin) |
1988 |
Piperidine | 110-89-4 | AIHA | 1 ppm (skin) | — | 1996 |
Polyethylene Glycols (MW > 200) | 25322-68-3 | AIHA | 10 mg/m3 | — | 2009 |
Polypropylene Glycols | 25322-69-4 | AIHA | 10 mg/m3 | 1997 | |
Potassium Bromate | 7758-01-2 | AIHA | 0.1 mg/m3 | 2004 | |
Propargyl Bromide | 106-96-7 | AIHA | 0.1 ppm (skin) | — | 1997 |
Propenoic Acid, isooctyl ester, 2- | 29590-42-9 | AIHA | 5 ppm | 2010 | |
Propionaldehyde | 123-38-6 | AIHA | 20 ppm | 2002 | |
Propylene Glycol | 57-55-6 | AIHA | 10 mg/m3 | 2004 | |
Propylene Glycol Monomethyl Ether Acetate | 108-65-6 | AIHA | 50 ppm | — | 2005 |
Quinoline | 91-22-5 | AIHA | 0.001 ppm (skin) | 2006 | |
Sodium Chloroacetate | 3926-62-3 | OARS | 0.5 ppm (2.5 mg/m3 ) | 2016 | |
Sodium Hypochlorite | 7681-52-9 | AIHA | 2 mg/m3 (15 min) | 2010 | |
Tetrachloropyridine, 2,3,5,6- | 2402-79-1 | OARS | 5 mg/m3 | 2016 | |
Tetrachlorosilane | 10026-04-7 | AIHA | 1 ppm (ceiling) | 1999 | |
Tetraethylene Glycol Diacrylate | 17831-71-9 | AIHA | 1 mg/m3 (skin, DSEN) | 1981 | |
TetraethylenePentamine | 112-57-2 | AIHA | 5 mg/m3 (skin, DSEN) | — | 2004 |
Tetrafluoroethane, 1,1,1,2- (HFC-134a) | 811-97-2 | AIHA | 1000 ppm | 2003 | |
Tetrafluoroethane, 1,1,2,2- (HFC-134) | 359-35-3 | OARS | 1000 ppm | 2018 | |
Tetrafluoroethane, 2-ChIoro-1,1,1,2- | 2837-89-0 | AIHA | 1000 ppm | — | 2005 |
Tetrafluoropropene, (Z)-1-ChIoro-2,3,3,3- (HCFO-1224yd(Z)) |
111512-60-8 | OARS | 1000 ppm | — | 2017 |
Tetrafluoropropene, 2,3,3,3,- (HFO-1234yf) | 754-12-1 | AIHA | 500 ppm | 2009 | |
Tetrafluoropropylene, 1,3,3,3- | 1645-83-6 | AIHA | 800 ppm | — | 2011 |
Tetrahydrofurfuryl Alcohol | 97-99-4 | AIHA | 0.5 ppm (skin) | 1993 | |
Titanium Tetrachloride | 7550-45-0 | AIHA | 0.5 mg/m3 | 2009 | |
Toluene Diamine, 2,4- and mixed isomers | 95-80-7; 25376- 45-8 |
AIHA | 0.005 ppm (skin) | 2010 | |
Toluenesulfonyl Chloride, para- | 98-59-9 | AIHA | 5 mg/m3 (ceiling) | 2009 | |
trans-1-Chloro-3,3,3-trifluoropropylene (HCFO 1233zd(E)) |
102687-65-0 | OARS | 800 ppm | 2013 | |
Trichlorosilane | 10025-78-2 | AIHA | 0.5 ppm (ceiling) | 1998 | |
Triethoxysilane | 998-30-1 | AIHA | 0.05 ppm | 2000 | |
Triethylene Glycol Diacrylate | 1680-21-3 | AIHA | 1 mg/m3 (skin) | 1981 | |
Triethylenetetramine | 112-24-3 | OARS | 1 ppm (skin) | 2023 | |
Triethylphosphate | 78-40-0 | AIHA | 7.45 mg/m3 | 2010 | |
TrifIuoro-2,2-Dichloroethane, 1,1,1- | 306-83-2 | AIHA | 50 ppm | 2001 | |
Trifluoroethane, 1,1,1- | 420-46-2 | AIHA | 1000 ppm | 1996 | |
Trifluoroethanol, 2,2,2- | 75-89-8 | OARS | 0.3 ppm | 2016 | |
Trifluoroiodomethane (CF3I) | 2314-97-8 | OARS | 500 ppm | 1500 ppm | 2018 |
Trimethoxysilane | 2487-90-3 | AIHA | 0.05 ppm | 2010 | |
Trimethylamine | 75-50-3 | AIHA | 1 ppm | 2005 | |
Trimethylchlorosilane | 75-77-4 | AIHA | 5 ppm (ceiling) | 2001 | |
Trimethylolpropane Triacrylate | 15625-89-5 | AIHA | 1 mg/m3 (skin) | 1981 | |
Trimethylolpropane Trimethacrylate | 3290-92-4 | AIHA | 1 mg/m3 (skin) | 1981 | |
Trisodium Phosphate | 7601-54-9 | AIHA | 5 mg/m3 (15 min) | 2009 | |
Urea | 57-13-6 | AIHA | 10 mg/m3 | 2007 | |
Vanillin | 121-33-5 | AIHA | 10 mg/m3 | 2009 | |
Vinylcyclohexene | 100-40-3 | AIHA | 1 ppm | 2009 | |
Vinyltrichlorosilane | 75-94-5 | AIHA | — | 1 ppm (ceiling) | 2002 |
*Value withdrawn
Substances Considered But Determined to Have an Inadequate Minimum Data Set:
Chlorine Monoxide
Methylene Butanedioic Acid
1,3-Pentadiene