Reference Source

Lookup · 802 substances

What is the OSHA exposure limit for this substance?

Find the exposure limit for a substance in workplace air — federal OSHA, California and NIOSH, side by side.

Sourcesosha.gov + dir.ca.gov + cdc.gov
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Where does this come from?

Straight from osha.gov, dir.ca.gov and cdc.gov. Every answer links the page it was read from and quotes the line on that page that says it, so you can check it yourself in one click. The full list is under Where this came from.

How do you know it's right?

Each value is checked back against its own source page: the number has to appear in the sentence we quote, and that sentence has to appear on the page. Anything that fails is fixed or left out rather than published. More on how that works.

How up to date is it?

We last checked every number here on . These change over time, so they are due to be checked again by — if that date passes, a notice appears at the top of the page.

8-Hour TWA Calculator — Find your 8-hour time-weighted average from air samples, and whether it is over the legal limit for that substance.

Cite as: US workplace chemical exposure limits: federal OSHA, Cal/OSHA and NIOSH, side by side, referencesource.org/workplace-exposure-limits/, checked 2026-08-05.

115 records where two or more sources state different values. Both sides are reproduced on the record page, each with its own source and quote.

About this data

Airborne exposure limits for workplace chemicals as stated by three independent authorities: federal OSHA's Table Z-1 (29 CFR 1910.1000), California's own Table AC-1 (8 CCR 5155), and NIOSH's Pocket Guide entry for the substance. Each record is one substance with the limit that agency publishes for it, the URL it came from and the verbatim line it was read from. **The product is the disagreement**: where more than one of them covers a substance the numbers are frequently far apart — acetone is 1000 ppm federally, 500 ppm in California and 250 ppm recommended by NIOSH; acetaldehyde is 200 ppm federally against 25 ppm in California; 1,1-dimethylhydrazine 0.5 against 0.01 — and exceeding a PEL is what triggers engineering controls, PPE and medical surveillance, so which number applies is consequential. OSHA's and California's are legal limits (PELs); NIOSH's is a recommendation (an REL), which is why it is carried in its own fields and never mixed into the PEL columns. Answers 'what is the exposure limit for [chemical]?', 'is the California PEL different from OSHA's?', 'what is the NIOSH REL for acetone' — the questions where an assistant gives one number without saying whose it is, or hands back an REL when it was asked for the legal limit.

802 records covering 799 substances, one fact each. Every value is transcribed from the source that states it and carries the sentence it was taken from: 649 sources across 3 sites, last checked 2026-08-05, due for re-check by 2027-08-05. Every record has a page of its own, quoting the line that states it.

SubstanceCAS No.PEL (ppm)PEL (mg/m³)NIOSH REL, as statedNIOSH REL (ppm)NIOSH REL (mg/m³)Ceiling notationSTEL (ppm)STEL (mg/m³)Ceiling
1,1,1,2-Tetrachloro-2,2-difluoroethane76-11-95004170TWA 5004170
1,1,1,2-Tetrachloroethane630-20-6Handle with caution in the workplace. See Appendix C (Chloroethanes)
1,1,2,2-Tetrachloro-1,2-difluoroethane76-12-05004170TWA 5004170
1,1,2,2-Tetrachloroethanesources differ79-34-5535TWA 17
1,1,2-Trichloro-1,2,2-trifluoroethane76-13-110007600TWA 10007600a ceiling value in addition to the TWA values125095002000 ppm
1,1,2-Trichloroethane79-00-51045TWA 1045
1,1-Dichloro-1-nitroethanesources differ594-72-9(C)10(C)60TWA 210
1,1-Dichloroethane75-34-3100400TWA 100400
1,1-Dimethylhydrazinesources differ57-14-70.51C 0.060.15
1,2,3-Trichloropropanesources differ96-18-450300TWA 1060
1,2,3-Trimethylbenzene526-73-8TWA 25125
1,2,4-Trichlorobenzene120821540C 540the values given in the PEL columns are ceiling values
1,2,4-Trimethylbenzene95-63-6TWA 25125
1,2-Dibromo-3-chloropropane96-12-8.001.01Ca See Appendix A
1,2-Dichloroethylene540-59-0200790TWA 200790
1,2-Dichlorotetrafluoroethane; Fluorocarbon 114761421,0007,000TWA 10007000
1,3,5-Triglycidyl-s-triazinetrione24516290.005
1,3,5-Trimethylbenzene108-67-8TWA 25125
1,3-Butadiene106-99-012.2Ca See Appendix A511
1,3-Dichloro-5,5-dimethyl hydantoin118-52-50.2TWA 0.20.4
1,3-Dichloropropene542-75-615TWA 15
1,4-Dichloro-2-butene7644100.0050.025
1,6-Hexanediamine1240940.52.3
1-bromopropane, n-propyl bromide106945525
1-Chloro-1-nitropropanesources differ600-25-920100TWA 210
1-Decanethiol143-10-2C 0.53.6
1-Dodecanethiol112-55-0C 0.54.1
1-Heptanethiol1639-09-4C 0.52.7
1-Hexadecanethiol2917-26-2C 0.55.3
1-Hexene59241650180
1-Nitropropane108-03-22590TWA 2590
1-Nonanethiol1455-21-6C 0.53.3
1-Octadecanethiol2885-00-9C 0.55.9
1-Octanethiol111-88-6C 0.53.0
1-Pentanethiol110-66-7C 0.52.1
1-Propanethiol107-03-9C 0.51.6
1-Undecanethiol5332-52-5C 0.53.9
2,2-Dichloropropionic acid7599016TWA 16
2,3,7,8-Tetrachloro-dibenzo-p-dioxin1746-01-6Ca See Appendix A
2,4,5-T93-76-510TWA 10
2,4,6-Trinitrotoluene118-96-71.5TWA 0.5
2,4-D94-75-710TWA 10
2,4-Diaminoanisole (and its salts)615-05-4Ca Minimize occupational exposure (especially skin exposures) See Appendix A
2,4-Dinitrotoluenesources differ253211460.15TWA 1.5
2,6-Di-tert-butyl-p-cresol12837010TWA 10
2-Acetylaminofluorene53-96-3Ca See Appendix A
2-Aminopyridine504-29-00.52TWA 0.52
2-Butanone78-93-3200590TWA 200590300885
2-Butoxyethanolsources differ111-76-250240TWA 524
2-Butoxyethanol acetate112-07-2TWA 533
2-Chloro-6-(trichloromethyl) pyridine1929-82-4TWA 10 mg/m3 (total) ST 20 mg/m3 (total) TWA 5 mg/m3 (resp)
2-Chloropropionic acid5987870.10.44
2-(Diethylamino) ethanolsources differ10037829.6TWA 1050
2-Ethoxyethanolsources differ110805518TWA 0.51.8
2-Ethoxyethyl acetatesources differ111159527TWA 0.52.7
2-Hexanone591-78-6100410TWA 141040
2-Hydroxypropyl acrylate9996110.53TWA 0.53
2-Isopropoxyethanol109-59-125105See Appendix D
2-Methoxyethanolsources differ109864516TWA 0.10.3
2-Methoxyethyl acetatesources differ110496524TWA 0.10.5
2-Methylbutyl acetate; see Pentyl acetate624419
2-Methylcyclopentadienyl manganese tricarbonyl, as Mn121081330.2TWA 0.2
2-N-Dibutylaminoethanol102818214TWA 214
2-Nitronaphthalene581-89-5Ca* See Appendix A
2-Nitropropanesources differ79-46-92590Ca See Appendix A
2-Pentanone107-87-9200700TWA 150530250875
3,3'-Dichlorobenzidine; 4,4'-diamino-3,3'-dichlorobiphenyl; see Section 520991941Ca See Appendix A
3-Amyl acetate; see Pentyl acetate620111
4,4′-Methylene bis(2-chloroaniline), see also Section 52151011440.01TWA 0.003
4,4′-Methylene dianiline; MDA (see also Sections 1535 & 5200)1017790.010.08Ca See Appendix A0.10.8
4,4′-Thiobis (6-tert, Butyl-m-cresol)96-69-5TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
4,6-Dinitro-o-cresol; 2-methyl-4,6-dinitrophenol5345210.2TWA 0.2
4-Aminodiphenyl92-67-1Ca See Appendix A
4-Dimethylaminoazobenzene60-11-7Ca See Appendix A
4-Methoxyphenol1507655TWA 5
4-Nitrobiphenyl92-93-3Ca See Appendix A
4-Vinyl cyclohexene1004030.10.4
5-Methyl-3-heptanone541-85-525130TWA 25130
a-Chloroacetophenone (Phenacyl chloride)532-27-40.050.30.05TWA 0.3
Acetaldehydesources differ75-07-0200360Ca See Appendix A See Appendix C (Aldehydes)the values given in the PEL columns are ceiling values
Acetic acid64-19-71025TWA 1025a ceiling value in addition to the TWA values153740 ppm
Acetic anhydride108-24-7520C 520the values given in the PEL columns are ceiling values
Acetonesources differ67-64-110002400TWA 250590a ceiling value in addition to the TWA values75017803000 ppm
Acetone cyanohydrin75-86-54.75C 14the values given in the PEL columns are ceiling values
Acetonitrile75-05-84070TWA 203460105
Acetophenone988621049
Acetylene74862C 25002662
Acetylene tetrabromide79-27-6114See Appendix D
Acetylsalicylic acid50-78-25TWA 5
Acrolein107-02-80.10.25TWA 0.10.25the values given in the PEL columns are ceiling values
Acrylamidesources differ79-06-10.3TWA 0.03
Acrylic acid7910725.9TWA 26
Acrylonitrile107-13-124.5TWA 1
Adipic acid1240495
Adiponitrile11169328.8TWA 418
Aldrin309-00-20.25TWA 0.25
Allyl alcoholsources differ107-18-625TWA 25410
Allyl chloride107-05-113TWA 1326
Allyl glycidyl ether106-92-3(C)10(C)45TWA 522
Allyl propyl disulfide2179-59-1212TWA 212318
alpha-Alumina1344-28-1See Appendix D
alpha-Methyl styrenesources differ98-83-9(C)100(C)480TWA 50240100485
alpha-Methylacrylonitrile12698713TWA 13
alpha-Naphthylamine134-32-7Ca See Appendix A
Aluminum7429-90-5TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Aluminum, alkyls (not otherwise classified)2
Aluminum distearate30092510
Aluminum pyro powders5
Aluminum soluble salts2
Aluminum stearate704784910
Aluminum tristearate63712710
Aluminum welding fumes5
Amitrole618250.2TWA 0.2
Ammoniasources differ7664-41-75035TWA 25183527
Ammonium chloride fume1212502910TWA 1020
Ammonium perfluorooctanoate38252610.01
Ammonium stearate100289710
Ammonium sulfamate7773-06-0TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Anilinesources differ6253327.6Ca See Appendix A
Anisidine (o-, p-isomers)29191-52-40.10.5
Antimony7440-36-00.5TWA 0.5
ANTU86-88-40.3TWA 0.3
Argon7440371
Arsenic and inorganic arsenic compounds; see also Section 521474403820.01
Arsenic (inorganic compounds, as As)7440-38-2 (metal)C 0.002
Arsenic, inorganic compounds (as As); see 1910.10187440-38-2
Arsenic, organic compounds (as As)sources differ7440-38-20.5
Arsine7784-42-10.050.2C 0.002
Asbestos1332-21-4Ca See Appendix A See Appendix C
Asphalt fumes8052-42-45C 5
Atrazine19122495TWA 5
Azinphos-methyl86-50-00.2TWA 0.2
Barium chloride (as Ba)10361-37-2TWA 0.5
Barium nitrate (as Ba)10022-31-8TWA 0.5
Barium, soluble compounds (as Ba)7440-39-30.5
Barium sulfate7727-43-7TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Benomyl17804-35-2See Appendix D
Benzene71-43-21TWA 0.15
Benzenethiol108-98-50.52C 0.10.5
Benzidine92-87-5Ca See Appendix A See Appendix C
Benzoyl chloride988840.21.1the values given in the PEL columns are ceiling values
Benzoyl peroxide94-36-05TWA 5
Benzyl acetate1401141061
Benzyl chloridesources differ100-44-715C 15
Beryllium, and beryllium compounds74404170.0002Ca See Appendix Aa ceiling value in addition to the TWA values0.0020.025mg/M3
beta-Chloroprenesources differ126-99-82590C 13.6
beta-Naphthylamine91-59-8Ca See Appendix A
beta-Propiolactone57-57-80.51.5Ca See Appendix A
Biphenyl; diphenyl; phenylbenzenesources differ925240.21.50.2TWA 1
bis(2-(Dimethylamino)ethyl)ether3033-62-30.050.328See Appendix C (NIAX® Catalyst ESN)0.150.983
bis-Chloromethyl ether542-88-10.0010.005Ca See Appendix A
Bismuth telluride1304821TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Bismuth telluride (selenium-doped)5
Borates, tetra, sodium salts (Anhydrous)1330-43-4TWA 1
Borates, tetra, sodium salts (Decahydrate)1303-96-4TWA 5
Borates, tetra, sodium salts (Pentahydrate)12179-04-3TWA 1
Boron oxide1303-86-210TWA 10
Boron tribromide10294334110C 110the values given in the PEL columns are ceiling values
Boron trifluoridesources differ7637-07-2(C)1(C)3C 13the values given in the PEL columns are ceiling values
Bromacil314409110TWA 110
Bromine7726-95-60.10.7TWA 0.10.7the values given in the PEL columns are ceiling values
Bromine pentafluoride77893020.10.7TWA 0.10.7
Bromoform75-25-20.55TWA 0.55
Butane1069788001,900TWA 8001900
Butyl acrylate141322211TWA 1055
Butyl mercaptansources differ109-79-51035C 0.51.8
Butylaminesources differ109-73-9(C)5(C)15C 515the values given in the PEL columns are ceiling values
Cadmium (as Cd); see 1910.10277440-43-9Ca See Appendix A
Cadmium fume (as Cd)1306-19-0 (CdO)Ca See Appendix A
Calcium arsenate (as As)7778-44-1C 0.002
Calcium carbonate1317-65-3
Calcium carbonate471-34-1 (synthetic) 1317-65-3 (natural)TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Calcium carbonate; see Particulates not otherwise regulated471341
Calcium cyanamide1566270.5TWA 0.5
Calcium hydroxide1305-62-05TWA 5
Calcium oxidesources differ1305-78-85TWA 2
Calcium silicate1344-95-2TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Calcium stearate159223010
Calcium sulfate7778-18-9TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Camphor, synthetic76-22-22TWA 2
Caprolactam105-60-2Dust: TWA 1 mg/m3 ST 3 mg/m3 Vapor: TWA 0.22 ppm (1 mg/m3) ST 0.66 ppm (3 mg/m3)
Caprolactam dust10560213
Caprolactam vapor1056025201040
Captafol24250610.1TWA 0.1
Captan1330625TWA 5
Carbaryl63-25-25TWA 5
Carbofuran15636620.1TWA 0.1
Carbon black1333-86-43.5TWA 3.5
Carbon dioxide124-38-950009000TWA 5000900030,00054,000
Carbon disulfide75-15-013TWA 13a ceiling value in addition to the TWA values123630 ppm
Carbon monoxidesources differ630-08-05055TWA 3540a ceiling value in addition to the TWA values200 ppm
Carbon tetrabromide5581340.11.4TWA 0.11.40.34
Carbon tetrachloride56-23-5212.6ST 212.6a ceiling value in addition to the TWA values1063200 ppm
Carbonyl fluoride35350425TWA 25515
Catechol120-80-9520TWA 520
Cellulose9004-34-6TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Cesium hydroxide213517912TWA 2
Chlordane57-74-90.5TWA 0.5
Chlorinated camphene8001-35-20.5Ca [skin] See Appendix A1
Chlorinated diphenyl oxide55720-99-50.5
Chlorinesources differ7782-50-5(C)1(C)3C 0.51.4513
Chlorine dioxide10049-04-40.10.3TWA 0.10.30.30.9
Chlorine trifluoridesources differ7790-91-2(C)0.1(C)0.4C 0.10.4the values given in the PEL columns are ceiling values
Chloroacetaldehydesources differ107-20-0(C)1(C)3C 13the values given in the PEL columns are ceiling values
Chloroacetone7895513.8the values given in the PEL columns are ceiling values
Chloroacetyl chloride790490.050.2TWA 0.050.20.150.69
Chlorobenzenesources differ108-90-775350See Appendix D
Chlorobromomethane74-97-52001050TWA 2001050
Chlorodifluoromethane75-45-61,0003,500TWA 10003500
Chlorodiphenyl (42% chlorine)534692191TWA 0.001
Chlorodiphenyl (54% chlorine)110976910.5TWA 0.001
Chloroform67-66-3(C)50(C)240ST 29.78
Chloromethyl methyl ether107-30-2Ca See Appendix A
Chloropentafluoroethane761531,0006,320TWA 10006320
Chloropicrin76-06-20.10.7TWA 0.10.7
Chlorpyrifos29218820.2TWA 0.2
Chromic acid and chromates1333-82-0 (CrO3)TWA 0.0002
Chromite ore processing (chromate), as Cr0.005
Chromium (II) compounds, as Cr0.5
Chromium (III) compounds, as Cr0.5
Chromium metalsources differ74404730.5TWA 0.5
Chromium (VI) compounds, as Cr0.005a ceiling value in addition to the TWA values0.1 mg/M3
Chromyl chloride149776180.0250.15Ca TWA 0.001 mg Cr(VI)/m3 See Appendix A See Appendix C
Clopidol2971-90-6TWA 10 mg/m3 (total) ST 20 mg/m3 (total) TWA 5 mg/m3 (resp)
Coal tar pitch volatiles65996-93-2TWA 0.1
Coal tar pitch volatiles (benzene soluble fraction), anthracene, BaP, phenanthrene, acridine, chrysene, pyrene65966-93-20.2
Coal tar pitch volatiles(i)0.2
Cobalt carbonyl (as Co)10210-68-10.1TWA 0.1
Cobalt hydrocarbonyl, as Co168420380.1TWA 0.1
Cobalt metal, dust, and fume (as Co)sources differ7440-48-40.1TWA 0.05
Coke oven emissions, see Section 52110.15
Copper7440-50-80.1TWA 1
Copper fume (as Cu)1317-38-0 (CuO)TWA 0.1
Copper salts, dusts and mists, as Cu1
Cotton dust, see also Section 51901(j)
Crag® herbicide136-78-7TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Cresol, all isomers1319-77-3522
Cristobalite,144644610.05
Crotonaldehyde4170-30-3TWA 26a ceiling value in addition to the TWA values0.3
Crufomate2998655TWA 5
Cumene98-82-850245TWA 50245
Cyanamide4200422TWA 2
Cyanide, as CN5
Cyanogen4601951020TWA 1020
Cyanogen chloride5067740.30.6C 0.30.6the values given in the PEL columns are ceiling values
Cyclohexane110-82-73001050TWA 3001050
Cyclohexanethiol1569-69-3C 0.52.4
Cyclohexanol108-93-050200TWA 50200
Cyclohexanonesources differ108-94-150200TWA 25100
Cyclohexene110-83-83001015TWA 3001015
Cyclohexylamine1089181040TWA 1040
Cyclonite121-82-40.07TWA 1.5
Cyclopentadiene542-92-775200TWA 75200
Cyclopentane2879236001,720TWA 6001720
Cyhexatin13121-70-55TWA 5
DDT50-29-31TWA 0.5
Decaborane17702-41-90.050.30.05TWA 0.30.150.9
Demeton8065-48-30.010.1TWA 0.1
Di-sec octyl phthalate117-81-75TWA 5
Diacetone alcohol123-42-250240TWA 50240
Diazinon®333-41-50.1TWA 0.1
Diazomethane334-88-30.20.4TWA 0.20.4
Diborane19287-45-70.10.1TWA 0.10.1
Dibutyl phenyl phosphate25283610.33.5
Dibutyl phosphate107-66-415TWA 15210
Dibutyl phthalate84-74-25TWA 5
Dichloroacetylene75722940.10.4C 0.10.4the values given in the PEL columns are ceiling values
Dichlorodifluoromethane75-71-810004950TWA 10004950a ceiling value in addition to the TWA values6200 ppm
Dichloroethyl ethersources differ111-44-4(C)15(C)90TWA 5301060
Dichlorofluoromethane; Fluorocarbon 21sources differ754341042TWA 1040
Dichlorvos62-73-70.11TWA 1
Dicrotophos1416620.25TWA 0.25
Dicyclopentadiene77736530TWA 530
Dicyclopentadienyl iron102-54-5TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Dieldrin60-57-10.25TWA 0.25
Diethanolamine1114220.462TWA 315
Diethyl ketone96220200705TWA 2007053001057
Diethyl phthalate846625TWA 5
Diethylaminesources differ109-89-72575TWA 1030the values given in the PEL columns are ceiling values
Diethylene glycol diethyl ether, Ethyl diglyme112367533
Diethylene glycol dimethyl ether, Diglyme11196615.5527
Diethylenetriamine111-40-014TWA 14
Difluorodibromomethane75-61-6100860TWA 100860
Diglycidyl ether2238-07-5(C)0.5(C)2.8TWA 0.10.5
Diisobutyl ketonesources differ108-83-850290TWA 25150
Diisopropylamine108-18-9520TWA 520
Dimethyl-1,2-dibromo-2,2-dichlorethyl phosphate300-76-53TWA 3
Dimethyl acetamide127-19-51035TWA 1035
Dimethyl carbamoyl chloride79-44-7Ca See Appendix A
Dimethyl phthalate1311135TWA 5
Dimethyl sulfatesources differ77-78-115TWA 0.10.5
Dimethylaminesources differ124-40-31018TWA 10181527.6
Dimethylaminopropionitrile1738-25-6See Appendix C (NIAX® Catalyst ESN)
Dimethylaniline (N,N-Dimethylaniline)121-69-7525TWA 5251050
Dimethylethoxysilane148573420.52.11.56.4
Dimethylformamide68-12-21030TWA 1030
Dinitolmide148-01-65TWA 5
Dinitrobenzene (all (isomers) ortho, meta and para isomers528290, 99650, 1002540.151
Dioxane123-91-1100360C 13.6
Dioxathion783420.2TWA 0.2
Diphenylamine122-39-410TWA 10
Dipropyl ketone12319350235TWA 50235
Dipropylene glycol methyl ether34590-94-8100600TWA 100600150900
Diquat; 1,1'-ethylene-2,2'-dipyridinium dibromide85007TWA 0.5
Disulfiram977782TWA 2
Disulfoton298-04-40.1TWA 0.1
Diuron33054110TWA 10
Divinyl benzene13217401050TWA 1050
Emery12415-34-8
Emery1302-74-5 (corundum)See Appendix D
Endosulfan115-29-70.1TWA 0.1
Endrin72-20-80.1TWA 0.1
Enflurane13838169215C 215.1
Epichlorohydrinsources differ106-89-8519Ca See Appendix A
EPNsources differ2104-64-50.5TWA 0.5
Ethane74840
Ethanolaminesources differ141-43-536TWA 38615
Ethion5631220.4TWA 0.4
Ethyl acetate141-78-64001400TWA 4001400
Ethyl acrylatesources differ140-88-525100Ca See Appendix A25100
Ethyl alcohol64-17-510001900TWA 10001900
Ethyl benzenesources differ100-41-4100435TWA 10043530130
Ethyl bromidesources differ74-96-4200890See Appendix D
Ethyl butyl ketone106-35-450230TWA 5023075345
Ethyl chloridesources differ75-00-310002600Handle with caution in the workplace. See Appendix C (Chloroethanes)
Ethyl cyanoacrylate70858500.21.02
Ethyl ether60-29-74001200See Appendix D5001500
Ethyl formate109-94-4100300TWA 100300
Ethyl mercaptansources differ75-08-1(C)10(C)25C 0.51.3
Ethyl silicatesources differ78-10-4100850TWA 1085
Ethyl tert-butyl ether637923521
Ethylaminesources differ75-04-71018TWA 1018the values given in the PEL columns are ceiling values
Ethylene74851
Ethylene chlorohydrinsources differ107-07-3516C 13the values given in the PEL columns are ceiling values
Ethylene dibromide106-93-40.131TWA 0.045the values given in the PEL columns are ceiling values
Ethylene dichloride107-06-214TWA 14a ceiling value in addition to the TWA values28200 ppm
Ethylene glycol107-21-140100See Appendix Dthe values given in the PEL columns are ceiling values
Ethylene glycol diethyl ether, 1,2-diethoxyethane629141524
Ethylene glycol dimethyl ether, 1,2-dimethoxyethane, Glyme11071413.7518
Ethylene glycol dinitrate628-96-6(C)0.2(C)1ST 0.10.1
Ethylene oxide75-21-812C 595
Ethylene thiourea96-45-7Ca Use encapsulated form. See Appendix A
Ethylenediamine107-15-31025TWA 1025
Ethyleneimine151-56-40.51Ca See Appendix A
Ethylidene norbornene16219753525C 525the values given in the PEL columns are ceiling values
Fenamiphos222249260.1TWA 0.1
Fensulfothion1159020.1TWA 0.1
Fenthion553890.2See Appendix D
Ferbam14484-64-110TWA 10
Ferrovanadium dust12604-58-91TWA 13
Flour dust0.5(s)
Fluorides, as F2.5
Fluorine7782-41-40.10.2TWA 0.10.2
Fluorotrichloromethane75-69-410005600C 10005600the values given in the PEL columns are ceiling values
Fluoroxene406-90-6C 210.3
Fonofos9442290.1TWA 0.1
Formaldehyde50-00-00.75TWA 0.0162
Formamide751271018TWA 1015
Formic acid64-18-659TWA 591019
Furfuralsources differ98-01-1520See Appendix D
Furfuryl alcoholsources differ98-00-050200TWA 10401560
Gasoline8006619300900Ca See Appendix A5001500
Germanium tetrahydride77826520.20.6TWA 0.20.6
Glass, fibrous1.0 f/cc(q)
Glutaraldehyde111-30-80.050.2C 0.20.8the values given in the PEL columns are ceiling values
Glycerin (mist)56-81-5See Appendix D
Glyceryl stearate12394410
Glycidolsources differ556-52-550150TWA 2575
Glycolonitrile107-16-4C 25
Glyoxal, 1,2-ethanedione1072220.1(s), (u)
Grain dust (oat, wheat, barley)10
Graphite (natural)7782-42-52.5TWA 2.5 mg/m3 (resp)
Graphite (synthetic)7440-44-0 (synthetic)See Appendix D
Gypsum13397-24-5TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
Hafnium7440-58-60.5TWA 0.5
Halothane151677216C 216.2
Helium7440597
Heptachlorsources differ76-44-80.5TWA 0.5
Heptane (n-Heptane)sources differ142-82-55002000TWA 853505002000
Hexachlorobenzene1187410.002
Hexachlorobutadiene876830.020.24TWA 0.020.24
Hexachlorocyclopentadiene774740.010.11TWA 0.010.1
Hexachloroethane67-72-1110TWA 110
Hexachloronaphthalene1335-87-10.2TWA 0.2
Hexafluoroacetone684-16-20.10.7TWA 0.10.7
Hexamethyl phosphoramide680-31-9Ca See Appendix A
Hexamethylene diisocyanate822-06-00.0050.034TWA 0.0050.035
Hexane, other isomers500180010003600
Hexone108-10-1100410TWA 5020575300
Hexylene glycol10741525125C 25125the values given in the PEL columns are ceiling values
Hydrazinesources differ302-01-211.3C 0.030.04
Hydrogen1333740
Hydrogen bromide10035-10-6310C 310the values given in the PEL columns are ceiling values
Hydrogen chloridesources differ7647-01-0(C)5(C)7C 57a ceiling value in addition to the TWA values2 ppm
Hydrogen cyanidesources differ74-90-81011ST 4.75the values given in the PEL columns are ceiling values
Hydrogen fluoride7664-39-30.40.33TWA 32.510.83
Hydrogen peroxide7722-84-111.4TWA 11.4
Hydrogen selenide7783-07-50.050.2TWA 0.050.2
Hydrogen sulfide7783-06-41014C 1015a ceiling value in addition to the TWA values152150 ppm
Hydrogenated terphenyls617883270.55TWA 0.55

NIOSH REL (ppm) per cdc.gov. NIOSH REL (mg/m³) per cdc.gov. Ceiling per dir.ca.gov. Ceiling notation per dir.ca.gov. STEL (ppm) per dir.ca.gov. STEL (mg/m³) per dir.ca.gov. PEL (ppm) per dir.ca.gov. PEL (mg/m³) per dir.ca.gov. NIOSH REL, as stated per cdc.gov. Each record page quotes each source's own line.

Showing the first 400 of 802 records. Every record has its own page, with its source and the quoted line that states it; these list the rest.

Where this came from

Every record above links the page it was taken from and quotes the sentence that states it. These are the 649 sources this dataset was assembled from.

Machine-readable

From your own code

Same records, same quotes, without scraping the page: refsource is on PyPI and npm. Each value comes back carrying the URL it was read from and the sentence on that page that states it — .source and .quote sit on the value itself rather than in a side channel, so the checking step is available instead of skipped.

pip install refsource
refsource lookup workplace-exposure-limits substance=1,1,1,2-Tetrachloro-2,2-difluoroethane

npx -y refsource lookup workplace-exposure-limits substance=1,1,1,2-Tetrachloro-2,2-difluoroethane

Set your AI assistant up to use this

Two files and no account. Put this in .mcp.json at the root of your project — Claude Code, Cursor, Windsurf, VS Code and Codex all read that file — and your assistant can look this dataset up instead of recalling it. The server is remote, keyless and read-only.

{
  "mcpServers": {
    "referencesource": {
      "type": "http",
      "url": "https://referencesource.org/mcp"
    }
  }
}

Add to Cursor · or, on the command line: claude mcp add --transport http referencesource https://referencesource.org/mcp --scope project

Then one line in the project's CLAUDE.md or AGENTS.md, so the assistant knows when to reach for it:

When a question needs "US workplace chemical exposure limits: federal OSHA, Cal/OSHA and NIOSH, side by side", call the referencesource MCP server at https://referencesource.org/mcp (tool `search_records`, dataset_slug `workplace-exposure-limits`) instead of answering from memory — every record it returns carries its source URL and a verbatim quote from that page.

What each tool does, and the servers built over single registers: Connect your AI assistant.

802 records. last verified against source . due for re-check by .

Licence. US federal and California government works — public domain. ACGIH TLVs deliberately excluded (copyrighted).