{
  "source": "https://respiratorcalculator.com",
  "license": "CC-BY-4.0",
  "reviewed": "2026-07-18",
  "note": "APF values are OSHA 29 CFR 1910.134 Table 1 (public federal law). Exposure limits cited from OSHA PELs and NIOSH RELs/IDLH — verify against the current primary source before use.",
  "apfTable": [
    {
      "id": "apr-quarter",
      "category": "APR",
      "categoryLabel": "Air-Purifying Respirator",
      "facepiece": "Quarter mask",
      "apf": 5
    },
    {
      "id": "apr-half",
      "category": "APR",
      "categoryLabel": "Air-Purifying Respirator",
      "facepiece": "Half mask",
      "apf": 10,
      "note": "Includes filtering facepiece & elastomeric half masks."
    },
    {
      "id": "apr-full",
      "category": "APR",
      "categoryLabel": "Air-Purifying Respirator",
      "facepiece": "Full facepiece",
      "apf": 50
    },
    {
      "id": "papr-half",
      "category": "PAPR",
      "categoryLabel": "Powered Air-Purifying Respirator",
      "facepiece": "Half mask",
      "apf": 50
    },
    {
      "id": "papr-full",
      "category": "PAPR",
      "categoryLabel": "Powered Air-Purifying Respirator",
      "facepiece": "Full facepiece",
      "apf": 1000
    },
    {
      "id": "papr-hood",
      "category": "PAPR",
      "categoryLabel": "Powered Air-Purifying Respirator",
      "facepiece": "Helmet / hood",
      "apf": 25,
      "note": "APF 25–1,000: an APF of 1,000 applies only with manufacturer WPF/SWPF evidence per §1910.134; otherwise treat as 25."
    },
    {
      "id": "papr-loose",
      "category": "PAPR",
      "categoryLabel": "Powered Air-Purifying Respirator",
      "facepiece": "Loose-fitting facepiece",
      "apf": 25
    },
    {
      "id": "sar-demand-half",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Half mask",
      "mode": "Demand",
      "apf": 10
    },
    {
      "id": "sar-demand-full",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Full facepiece",
      "mode": "Demand",
      "apf": 50
    },
    {
      "id": "sar-cf-half",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Half mask",
      "mode": "Continuous flow",
      "apf": 50
    },
    {
      "id": "sar-cf-full",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Full facepiece",
      "mode": "Continuous flow",
      "apf": 1000
    },
    {
      "id": "sar-cf-hood",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Helmet / hood",
      "mode": "Continuous flow",
      "apf": 25,
      "note": "APF 25–1,000: an APF of 1,000 applies only with manufacturer WPF/SWPF evidence per §1910.134; otherwise treat as 25."
    },
    {
      "id": "sar-cf-loose",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Loose-fitting facepiece",
      "mode": "Continuous flow",
      "apf": 25
    },
    {
      "id": "sar-pd-half",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Half mask",
      "mode": "Pressure-demand / positive-pressure",
      "apf": 50
    },
    {
      "id": "sar-pd-full",
      "category": "SAR",
      "categoryLabel": "Supplied-Air Respirator (Airline)",
      "facepiece": "Full facepiece",
      "mode": "Pressure-demand / positive-pressure",
      "apf": 1000,
      "idlhCapable": true,
      "note": "Permitted for IDLH atmospheres only in combination with an auxiliary self-contained air supply (§1910.134(d)(2))."
    },
    {
      "id": "scba-demand-half",
      "category": "SCBA",
      "categoryLabel": "Self-Contained Breathing Apparatus",
      "facepiece": "Half mask",
      "mode": "Demand",
      "apf": 10
    },
    {
      "id": "scba-demand-full",
      "category": "SCBA",
      "categoryLabel": "Self-Contained Breathing Apparatus",
      "facepiece": "Full facepiece",
      "mode": "Demand",
      "apf": 50
    },
    {
      "id": "scba-pd-full",
      "category": "SCBA",
      "categoryLabel": "Self-Contained Breathing Apparatus",
      "facepiece": "Full facepiece",
      "mode": "Pressure-demand / positive-pressure",
      "apf": 10000,
      "idlhCapable": true,
      "note": "NIOSH-certified full-facepiece pressure-demand SCBA (≥30 min) is permitted for IDLH atmospheres (§1910.134(d)(2))."
    }
  ],
  "substances": [
    {
      "slug": "ammonia",
      "name": "Ammonia",
      "formula": "NH3",
      "casNumber": "7664-41-7",
      "molecularWeight": 17.03,
      "oshaPEL": {
        "value": 50,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 25,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "idlh": {
        "value": 300,
        "unit": "ppm"
      },
      "commonUses": "Refrigerant, fertilizer production, and industrial/household cleaners; agriculture, refrigeration, and chemical manufacturing.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 25 ppm, ST 35 ppm. OSHA PEL TWA 50 ppm (Table Z-1). IDLH 300 ppm. NPG conversion 1 ppm = 0.70 mg/m3; MW listed 17.0 (precise 17.03).",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0028.html",
        "https://www.cdc.gov/niosh/idlh/7664417.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "carbon-monoxide",
      "name": "Carbon monoxide",
      "formula": "CO",
      "casNumber": "630-08-0",
      "molecularWeight": 28.01,
      "oshaPEL": {
        "value": 50,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 35,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "idlh": {
        "value": 1200,
        "unit": "ppm"
      },
      "commonUses": "Combustion byproduct of engines, furnaces, and heaters; steel/metal production, mining, vehicle repair, and firefighting.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 35 ppm, Ceiling 200 ppm. OSHA PEL TWA 50 ppm (Table Z-1). IDLH 1,200 ppm (current; older 1,500 ppm superseded). NPG conversion 1 ppm = 1.15 mg/m3; MW 28.0 (precise 28.01).",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0105.html",
        "https://www.cdc.gov/niosh/idlh/630080.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "chlorine",
      "name": "Chlorine",
      "formula": "Cl2",
      "casNumber": "7782-50-5",
      "molecularWeight": 70.9,
      "oshaPEL": {
        "value": 1,
        "unit": "ppm",
        "type": "Ceiling"
      },
      "nioshREL": {
        "value": 0.5,
        "unit": "ppm",
        "type": "Ceiling (15-minute)"
      },
      "idlh": {
        "value": 10,
        "unit": "ppm"
      },
      "commonUses": "Water and wastewater disinfection, household/industrial bleach, and PVC/plastics and chemical manufacturing.",
      "confidence": "high",
      "notes": "NIOSH REL Ceiling 0.5 ppm [15-min]. OSHA PEL Ceiling 1 ppm (Table Z-1). IDLH 10 ppm. Neither agency sets an 8-hr TWA. NPG conversion 1 ppm = 2.90 mg/m3; MW 70.9.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0115.html",
        "https://www.cdc.gov/niosh/idlh/7782505.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "hydrogen-sulfide",
      "name": "Hydrogen sulfide",
      "formula": "H2S",
      "casNumber": "7783-06-4",
      "molecularWeight": 34.08,
      "oshaPEL": {
        "value": 20,
        "unit": "ppm",
        "type": "Ceiling"
      },
      "nioshREL": {
        "value": 10,
        "unit": "ppm",
        "type": "Ceiling (10-minute)"
      },
      "idlh": {
        "value": 100,
        "unit": "ppm"
      },
      "commonUses": "Oil & gas (sour gas) production and refining, wastewater/sewer systems, pulp & paper, and mining.",
      "confidence": "high",
      "notes": "OSHA PEL (Table Z-2) Ceiling 20 ppm with 50 ppm acceptable maximum peak for a single 10-min period per 8-hr shift. NIOSH REL Ceiling 10 ppm [10-min]. IDLH 100 ppm. NPG conversion 1 ppm = 1.40 mg/m3; MW 34.1. Sense of smell fatigues rapidly and cannot be relied on as a warning.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0337.html",
        "https://www.cdc.gov/niosh/idlh/7783064.html",
        "https://www.osha.gov/annotated-pels/table-z-2"
      ]
    },
    {
      "slug": "sulfur-dioxide",
      "name": "Sulfur dioxide",
      "formula": "SO2",
      "casNumber": "7446-09-5",
      "molecularWeight": 64.07,
      "oshaPEL": {
        "value": 5,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 2,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "idlh": {
        "value": 100,
        "unit": "ppm"
      },
      "commonUses": "Fossil-fuel combustion and ore smelting emissions, pulp/paper bleaching, and use as a food preservative and fumigant.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 2 ppm, ST 5 ppm. OSHA PEL TWA 5 ppm (Table Z-1). IDLH 100 ppm. NPG conversion 1 ppm = 2.62 mg/m3; MW 64.1.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0575.html",
        "https://www.cdc.gov/niosh/idlh/7446095.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "nitrogen-dioxide",
      "name": "Nitrogen dioxide",
      "formula": "NO2",
      "casNumber": "10102-44-0",
      "molecularWeight": 46.01,
      "oshaPEL": {
        "value": 5,
        "unit": "ppm",
        "type": "Ceiling"
      },
      "nioshREL": {
        "value": 1,
        "unit": "ppm",
        "type": "STEL (15-minute)"
      },
      "idlh": {
        "value": 13,
        "unit": "ppm"
      },
      "commonUses": "Welding and combustion/diesel-exhaust environments, silo/agriculture (silo gas), and nitric acid/explosives manufacturing.",
      "confidence": "high",
      "notes": "NIOSH REL STEL 1 ppm; NIOSH sets no 8-hr TWA. OSHA PEL Ceiling 5 ppm (Table Z-1). IDLH revised to 13 ppm (NPG cites 2017-202; older 20 ppm superseded). NPG conversion 1 ppm = 1.88 mg/m3; MW 46.0.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0454.html",
        "https://www.cdc.gov/niosh/idlh/10102440.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "ozone",
      "name": "Ozone",
      "formula": "O3",
      "casNumber": "10028-15-6",
      "molecularWeight": 48,
      "oshaPEL": {
        "value": 0.1,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 0.1,
        "unit": "ppm",
        "type": "Ceiling"
      },
      "idlh": {
        "value": 5,
        "unit": "ppm"
      },
      "commonUses": "Water and air disinfection/ozonation, welding fume, laser printers/photocopiers, and semiconductor and food processing.",
      "confidence": "high",
      "notes": "NIOSH REL Ceiling 0.1 ppm (sole REL in current NPG). OSHA PEL 8-hr TWA 0.1 ppm (Table Z-1). IDLH 5 ppm. NPG conversion 1 ppm = 1.96 mg/m3; MW 48.0. Do not publish the older workload-dependent REL values (e.g., 0.20 ppm heavy work up to 2 hr) — they are from superseded criteria documentation, not the current NPG.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0476.html",
        "https://www.cdc.gov/niosh/idlh/10028156.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "carbon-dioxide",
      "name": "Carbon dioxide",
      "formula": "CO2",
      "casNumber": "124-38-9",
      "molecularWeight": 44.01,
      "oshaPEL": {
        "value": 5000,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 5000,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "idlh": {
        "value": 40000,
        "unit": "ppm"
      },
      "commonUses": "Welding shielding gas, beverage carbonation, dry ice, and fire suppression; a confined-space asphyxiation hazard.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 5,000 ppm, ST 30,000 ppm. OSHA PEL TWA 5,000 ppm (Table Z-1). IDLH 40,000 ppm (4%). NPG conversion 1 ppm = 1.80 mg/m3; MW 44.0.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0103.html",
        "https://www.cdc.gov/niosh/idlh/124389.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "benzene",
      "name": "Benzene",
      "formula": "C6H6",
      "casNumber": "71-43-2",
      "molecularWeight": 78.1,
      "oshaPEL": {
        "value": 1,
        "unit": "ppm",
        "type": "TWA 8-hr (29 CFR 1910.1028; also STEL 5 ppm over 15 min)"
      },
      "nioshREL": {
        "value": 0.1,
        "unit": "ppm",
        "type": "TWA (potential occupational carcinogen, Ca; also STEL 1 ppm)"
      },
      "idlh": {
        "value": 500,
        "unit": "ppm"
      },
      "commonUses": "Solvent and chemical feedstock (styrene, phenol, cumene), gasoline component; petroleum refining, petrochemicals, coke/steel.",
      "confidence": "high",
      "notes": "REL Ca TWA 0.1 ppm ST 1 ppm; PEL TWA 1 ppm ST 5 ppm (substance-specific standard 1910.1028, not Z-1). IDLH Ca [500 ppm] (older 3,000 ppm obsolete). NPG conversion 1 ppm = 3.19 mg/m3; MW 78.1. Potential occupational carcinogen (NIOSH Appendix A).",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0049.html",
        "https://www.cdc.gov/niosh/idlh/71432.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "toluene",
      "name": "Toluene",
      "formula": "C7H8",
      "casNumber": "108-88-3",
      "molecularWeight": 92.1,
      "oshaPEL": {
        "value": 200,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-2; plus Ceiling 300 ppm and 500 ppm 10-min maximum peak)"
      },
      "nioshREL": {
        "value": 100,
        "unit": "ppm",
        "type": "TWA (also STEL 150 ppm)"
      },
      "idlh": {
        "value": 500,
        "unit": "ppm"
      },
      "commonUses": "Solvent in paints, coatings, adhesives, inks; gasoline component; chemical intermediate. Printing, coatings, chemical manufacturing.",
      "confidence": "high",
      "notes": "REL TWA 100 ppm (375 mg/m3) ST 150 ppm (560 mg/m3); PEL is a Table Z-2 multi-part limit TWA 200/C 300/500 ppm 10-min peak. IDLH 500 ppm. NPG conversion 1 ppm = 3.77 mg/m3; MW 92.1.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0619.html",
        "https://www.cdc.gov/niosh/idlh/108883.html",
        "https://www.osha.gov/annotated-pels/table-z-2"
      ]
    },
    {
      "slug": "xylenes",
      "name": "Xylenes (o-, m-, p-isomers)",
      "formula": "C8H10",
      "casNumber": "1330-20-7 (mixed); o- 95-47-6, m- 108-38-3, p- 106-42-3",
      "molecularWeight": 106.2,
      "oshaPEL": {
        "value": 100,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-1; ~435 mg/m3)"
      },
      "nioshREL": {
        "value": 100,
        "unit": "ppm",
        "type": "TWA (also STEL 150 ppm)"
      },
      "idlh": {
        "value": 900,
        "unit": "ppm"
      },
      "commonUses": "General-purpose solvent in paints, coatings, adhesives, printing; chemical intermediate (phthalic anhydride, PET). Coatings, printing, petrochemicals.",
      "confidence": "high",
      "notes": "All three isomers: REL TWA 100 ppm (435 mg/m3) ST 150 ppm (655 mg/m3); PEL TWA 100 ppm; IDLH 900 ppm; MW 106.2. Per-isomer ppm to mg/m3 conversion differs: o-/m- = 4.34, p- = 4.41 (genuine NPG rounding quirk). Mixed-xylenes CAS 1330-20-7. OSHA Z-1 has TWA only; the 150 ppm STEL is the NIOSH value.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0668.html",
        "https://www.cdc.gov/niosh/npg/npgd0669.html",
        "https://www.cdc.gov/niosh/npg/npgd0670.html",
        "https://www.cdc.gov/niosh/idlh/95476.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "methanol",
      "name": "Methanol",
      "formula": "CH4O",
      "casNumber": "67-56-1",
      "molecularWeight": 32.1,
      "oshaPEL": {
        "value": 200,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-1; 260 mg/m3)"
      },
      "nioshREL": {
        "value": 200,
        "unit": "ppm",
        "type": "TWA [skin] (also STEL 250 ppm)"
      },
      "idlh": {
        "value": 6000,
        "unit": "ppm"
      },
      "commonUses": "Solvent, antifreeze/de-icer, fuel and fuel additive, windshield-washer fluid, and feedstock (formaldehyde, biodiesel). Chemical manufacturing.",
      "confidence": "high",
      "notes": "REL TWA 200 ppm (260 mg/m3) ST 250 ppm (325 mg/m3) [skin]; PEL TWA 200 ppm; IDLH 6,000 ppm; MW 32.1; conversion 1 ppm = 1.31 mg/m3. NIOSH REL carries [skin] (dermal absorption) notation.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0397.html",
        "https://www.cdc.gov/niosh/idlh/67561.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "acetone",
      "name": "Acetone",
      "formula": "C3H6O",
      "casNumber": "67-64-1",
      "molecularWeight": 58.1,
      "oshaPEL": {
        "value": 1000,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-1; 2400 mg/m3)"
      },
      "nioshREL": {
        "value": 250,
        "unit": "ppm",
        "type": "TWA"
      },
      "idlh": {
        "value": 2500,
        "unit": "ppm"
      },
      "commonUses": "Solvent for cleaning/degreasing, nail-polish remover, resin/adhesive thinner; chemical intermediate (MMA, bisphenol-A). Coatings, plastics, labs.",
      "confidence": "high",
      "notes": "REL TWA 250 ppm (590 mg/m3) with no NIOSH STEL; PEL TWA 1,000 ppm; IDLH 2,500 ppm [10% LEL] (limited by lower explosive limit, not toxicity); MW 58.1; conversion 1 ppm = 2.38 mg/m3. An OSHA-table auto-summary erroneously reported REL 500/750/3000; raw NPG confirms REL is TWA 250 ppm.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0004.html",
        "https://www.cdc.gov/niosh/idlh/67641.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "methylene-chloride",
      "name": "Methylene chloride (Dichloromethane)",
      "formula": "CH2Cl2",
      "casNumber": "75-09-2",
      "molecularWeight": 84.9,
      "oshaPEL": {
        "value": 25,
        "unit": "ppm",
        "type": "TWA 8-hr (29 CFR 1910.1052; also STEL 125 ppm over 15 min)"
      },
      "idlh": {
        "value": 2300,
        "unit": "ppm"
      },
      "commonUses": "Paint stripper/remover, metal degreaser, solvent, aerosol propellant, foam blowing, extraction. Coatings, pharma, manufacturing.",
      "confidence": "high",
      "notes": "NIOSH REL is Ca [See Appendix A] — potential occupational carcinogen, no numeric REL (reduce to lowest feasible concentration); nioshREL field intentionally omitted. OSHA PEL TWA 25 ppm ST 125 ppm (substance-specific standard 1910.1052). IDLH Ca [2,300 ppm]. MW 84.9; conversion 1 ppm = 3.47 mg/m3.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0414.html",
        "https://www.cdc.gov/niosh/idlh/75092.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "styrene",
      "name": "Styrene",
      "formula": "C8H8",
      "casNumber": "100-42-5",
      "molecularWeight": 104.2,
      "oshaPEL": {
        "value": 100,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-2; plus Ceiling 200 ppm and 600 ppm 5-min peak in any 3 hrs)"
      },
      "nioshREL": {
        "value": 50,
        "unit": "ppm",
        "type": "TWA (also STEL 100 ppm)"
      },
      "idlh": {
        "value": 700,
        "unit": "ppm"
      },
      "commonUses": "Monomer for polystyrene, ABS, SBR rubber, and unsaturated polyester/fiberglass-reinforced plastics. Plastics, composites, boat/tub fabrication.",
      "confidence": "high",
      "notes": "REL TWA 50 ppm (215 mg/m3) ST 100 ppm (425 mg/m3); PEL is a Table Z-2 multi-part limit TWA 100/C 200/600 ppm 5-min peak; IDLH 700 ppm; MW 104.2; conversion 1 ppm = 4.26 mg/m3.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0571.html",
        "https://www.cdc.gov/niosh/idlh/100425.html",
        "https://www.osha.gov/annotated-pels/table-z-2"
      ]
    },
    {
      "slug": "tetrachloroethylene",
      "name": "Tetrachloroethylene (Perchloroethylene)",
      "formula": "C2Cl4",
      "casNumber": "127-18-4",
      "molecularWeight": 165.8,
      "oshaPEL": {
        "value": 100,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-2; plus Ceiling 200 ppm for 5 min in any 3-hr period and 300 ppm maximum peak)"
      },
      "idlh": {
        "value": 150,
        "unit": "ppm"
      },
      "commonUses": "Dry-cleaning solvent, metal vapor degreasing, textile processing, chemical intermediate. Dry cleaning, metalworking.",
      "confidence": "high",
      "notes": "NIOSH REL is Ca — potential occupational carcinogen, minimize workplace exposure, no numeric REL; nioshREL field intentionally omitted. OSHA PEL is a Table Z-2 multi-part limit TWA 100/C 200/300 ppm 5-min peak. IDLH Ca [150 ppm]; MW 165.8; conversion 1 ppm = 6.78 mg/m3.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0599.html",
        "https://www.cdc.gov/niosh/idlh/127184.html",
        "https://www.osha.gov/annotated-pels/table-z-2"
      ]
    },
    {
      "slug": "formaldehyde",
      "name": "Formaldehyde",
      "formula": "HCHO (CH2O)",
      "casNumber": "50-00-0",
      "molecularWeight": 30.03,
      "oshaPEL": {
        "value": 0.75,
        "unit": "ppm",
        "type": "TWA 8-hr (29 CFR 1910.1048; also STEL 2 ppm, action level 0.5 ppm)"
      },
      "nioshREL": {
        "value": 0.016,
        "unit": "ppm",
        "type": "TWA (carcinogen, Ca; also 15-min Ceiling 0.1 ppm)"
      },
      "idlh": {
        "value": 20,
        "unit": "ppm"
      },
      "commonUses": "Resins/adhesives, particleboard & plywood, embalming/pathology, textiles, disinfectants; wood-products and healthcare industries.",
      "confidence": "high",
      "notes": "Verified via NIOSH IDLH page + NPG search data (live NPG card fetch was 403 — re-verify card directly). OSHA 1910.1048: TWA 0.75 ppm, STEL 2 ppm, action level 0.5 ppm. NIOSH REL Ca: TWA 0.016 ppm with 15-min Ceiling 0.1 ppm. IDLH Ca [20 ppm]. Conversion 1 ppm = 1.23 mg/m3; MW 30.0.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0293.html",
        "https://www.cdc.gov/niosh/idlh/50000.html",
        "https://www.osha.gov/annotated-pels/table-z-1",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1048"
      ]
    },
    {
      "slug": "hydrogen-chloride",
      "name": "Hydrogen chloride",
      "formula": "HCl",
      "casNumber": "7647-01-0",
      "molecularWeight": 36.46,
      "oshaPEL": {
        "value": 5,
        "unit": "ppm",
        "type": "Ceiling"
      },
      "nioshREL": {
        "value": 5,
        "unit": "ppm",
        "type": "Ceiling"
      },
      "idlh": {
        "value": 50,
        "unit": "ppm"
      },
      "commonUses": "Steel pickling, chemical manufacturing, metal etching, oil-well acidizing, water treatment; anhydrous gas and aqueous (muriatic/hydrochloric acid).",
      "confidence": "high",
      "notes": "Both NIOSH REL and OSHA PEL are Ceiling 5 ppm (7 mg/m3), not to be exceeded at any time. IDLH 50 ppm on the current NPG card. IMPORTANT: NIOSH published a revised IDLH Value Profile in 2025 (DHHS/NIOSH Pub 2025-110) lowering the calculated IDLH to 45 ppm; NPG card not yet updated at check time — treat 45 ppm as the more current NIOSH figure. Conversion 1 ppm = 1.49 mg/m3; MW 36.5.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0332.html",
        "https://www.osha.gov/annotated-pels/table-z-1",
        "https://www.cdc.gov/niosh/docs/2025-110/pdfs/2025-110revised062025.pdf"
      ]
    },
    {
      "slug": "hydrogen-fluoride",
      "name": "Hydrogen fluoride",
      "formula": "HF",
      "casNumber": "7664-39-3",
      "molecularWeight": 20.01,
      "oshaPEL": {
        "value": 3,
        "unit": "ppm",
        "type": "TWA 8-hr (Table Z-2)"
      },
      "nioshREL": {
        "value": 3,
        "unit": "ppm",
        "type": "TWA 8-hr (also 15-min Ceiling 6 ppm)"
      },
      "idlh": {
        "value": 30,
        "unit": "ppm"
      },
      "commonUses": "Aluminum production, glass/semiconductor etching, stainless-steel pickling, petroleum alkylation catalyst, fluorochemical manufacture.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 3 ppm (2.5 mg/m3) AND 15-min Ceiling 6 ppm (5 mg/m3). OSHA PEL (Table Z-2) TWA 3 ppm. Values expressed as HF. IDLH 30 ppm. Conversion 1 ppm = 0.82 mg/m3; MW 20.0.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0334.html",
        "https://www.cdc.gov/niosh/idlh/7664393.html",
        "https://www.osha.gov/annotated-pels/table-z-2"
      ]
    },
    {
      "slug": "ethylene-oxide",
      "name": "Ethylene oxide",
      "formula": "C2H4O",
      "casNumber": "75-21-8",
      "molecularWeight": 44.05,
      "oshaPEL": {
        "value": 1,
        "unit": "ppm",
        "type": "TWA 8-hr (29 CFR 1910.1047; also 15-min Excursion Limit 5 ppm)"
      },
      "nioshREL": {
        "value": 0.1,
        "unit": "ppm",
        "type": "TWA (carcinogen, Ca; <0.1 ppm, also 5 ppm Ceiling [10-min/day])"
      },
      "idlh": {
        "value": 800,
        "unit": "ppm"
      },
      "commonUses": "Sterilization of heat-sensitive medical devices, fumigant, and chemical intermediate (ethylene glycol, surfactants); healthcare and chemical industries.",
      "confidence": "high",
      "notes": "OSHA 1910.1047: TWA 1 ppm plus 5 ppm 15-min Excursion Limit. NIOSH REL Ca: TWA <0.1 ppm (0.18 mg/m3) with 5 ppm Ceiling [10-min/day]. IDLH Ca [800 ppm]. Conversion 1 ppm = 1.80 mg/m3; MW 44.1.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0275.html",
        "https://www.cdc.gov/niosh/idlh/75218.html",
        "https://www.osha.gov/annotated-pels/table-z-1",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1047"
      ]
    },
    {
      "slug": "methyl-ethyl-ketone",
      "name": "Methyl ethyl ketone (2-Butanone, MEK)",
      "formula": "CH3COCH2CH3 (C4H8O)",
      "casNumber": "78-93-3",
      "molecularWeight": 72.11,
      "oshaPEL": {
        "value": 200,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 200,
        "unit": "ppm",
        "type": "TWA 8-hr (also STEL 300 ppm)"
      },
      "idlh": {
        "value": 3000,
        "unit": "ppm"
      },
      "commonUses": "Solvent in paints, coatings, adhesives, printing inks, and lacquers; degreasing and resin/rubber processing.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 200 ppm (590 mg/m3) AND STEL 300 ppm (885 mg/m3). OSHA PEL TWA 200 ppm (590 mg/m3). IDLH 3,000 ppm. Conversion 1 ppm = 2.95 mg/m3; MW 72.1.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0069.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "isopropyl-alcohol",
      "name": "Isopropyl alcohol (2-Propanol, IPA)",
      "formula": "(CH3)2CHOH (C3H8O)",
      "casNumber": "67-63-0",
      "molecularWeight": 60.1,
      "oshaPEL": {
        "value": 400,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 400,
        "unit": "ppm",
        "type": "TWA 8-hr (also STEL 500 ppm)"
      },
      "idlh": {
        "value": 2000,
        "unit": "ppm"
      },
      "commonUses": "Solvent, surface disinfectant/cleaner (rubbing alcohol), electronics cleaning, pharmaceutical and cosmetic manufacturing.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 400 ppm (980 mg/m3) AND STEL 500 ppm (1225 mg/m3). OSHA PEL TWA 400 ppm (980 mg/m3). IDLH 2,000 ppm [10% LEL]. Conversion 1 ppm = 2.46 mg/m3; MW 60.1.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0359.html",
        "https://www.cdc.gov/niosh/idlh/67630.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "nitric-acid",
      "name": "Nitric acid",
      "formula": "HNO3",
      "casNumber": "7697-37-2",
      "molecularWeight": 63.01,
      "oshaPEL": {
        "value": 2,
        "unit": "ppm",
        "type": "TWA 8-hr"
      },
      "nioshREL": {
        "value": 2,
        "unit": "ppm",
        "type": "TWA 8-hr (also STEL 4 ppm)"
      },
      "idlh": {
        "value": 25,
        "unit": "ppm"
      },
      "commonUses": "Fertilizer (ammonium nitrate) and explosives manufacture, metal etching/pickling, electronics, and oxidizer production.",
      "confidence": "high",
      "notes": "NIOSH REL TWA 2 ppm (5 mg/m3) AND STEL 4 ppm (10 mg/m3). OSHA PEL TWA 2 ppm (5 mg/m3). IDLH 25 ppm. Conversion 1 ppm = 2.58 mg/m3; MW 63.0.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0447.html",
        "https://www.cdc.gov/niosh/idlh/7697372.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "hydrogen-cyanide",
      "name": "Hydrogen cyanide",
      "formula": "HCN",
      "casNumber": "74-90-8",
      "molecularWeight": 27.03,
      "oshaPEL": {
        "value": 10,
        "unit": "ppm",
        "type": "TWA 8-hr [skin]"
      },
      "nioshREL": {
        "value": 4.7,
        "unit": "ppm",
        "type": "STEL (ST) [skin], 10-minute short-term/ceiling"
      },
      "idlh": {
        "value": 50,
        "unit": "ppm"
      },
      "commonUses": "Manufacture of acrylonitrile/adiponitrile and other nitriles, electroplating, metal treatment, gold/silver extraction, and fumigation.",
      "confidence": "high",
      "notes": "NIOSH REL is a 4.7 ppm (5 mg/m3) [skin] short-term/ceiling limit (10-min), NOT an 8-hr TWA — label carefully. OSHA PEL TWA 10 ppm (11 mg/m3) [skin]. IDLH 50 ppm. Conversion 1 ppm = 1.10 mg/m3; MW 27.0. 'skin' = danger of skin absorption. (ACGIH TLV is 10 ppm Ceiling [skin] — not an OSHA/NIOSH value.)",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0333.html",
        "https://www.cdc.gov/niosh/idlh/74908.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ]
    },
    {
      "slug": "respirable-crystalline-silica",
      "name": "Respirable crystalline silica",
      "particulate": true,
      "formula": "SiO2",
      "casNumber": "14808-60-7",
      "oshaPEL": {
        "value": 0.05,
        "unit": "mg/m3",
        "type": "8-hr TWA, respirable fraction (substance-specific standard); action level 0.025 mg/m3"
      },
      "nioshREL": {
        "value": 0.05,
        "unit": "mg/m3",
        "type": "TWA (up to 10-hr), respirable; NIOSH Ca (potential occupational carcinogen)"
      },
      "idlh": {
        "value": 50,
        "unit": "mg/m3"
      },
      "oshaStandard": "29 CFR 1910.1053 (general industry & maritime); 29 CFR 1926.1153 (construction)",
      "filterNote": "Respirable solid mineral particulate, non-oil aerosol - N/R/P series all technically acceptable; N-series (e.g., N95) is the minimum, but N100/P100 (HEPA-level) is strongly recommended because quartz is a carcinogen and blasting/cutting generate very high concentrations. Select filter/respirator by assigned protection factor for the measured airborne level.",
      "commonUses": "Mining, quarrying, foundries, abrasive/sand blasting, concrete and masonry cutting/grinding, tunneling, brick and refractory work, and engineered-stone/natural-stone countertop fabrication (a major modern silicosis source).",
      "notes": "The current enforceable PEL is the 0.05 mg/m3 (50 ug/m3) 8-hr TWA under 1910.1053, which replaced the old formula limits in Table Z-3. IDLH 50 mg/m3 applies to quartz; cristobalite and tridymite have a lower 25 mg/m3 IDLH. Reference-only, not a substitute for a formal exposure assessment.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0684.html",
        "https://www.cdc.gov/niosh/idlh/14808607.html",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1053"
      ],
      "confidence": "high"
    },
    {
      "slug": "lead",
      "name": "Lead",
      "particulate": true,
      "formula": "Pb",
      "casNumber": "7439-92-1",
      "oshaPEL": {
        "value": 0.05,
        "unit": "mg/m3",
        "type": "8-hr TWA (as Pb); action level 0.03 mg/m3"
      },
      "nioshREL": {
        "value": 0.05,
        "unit": "mg/m3",
        "type": "TWA (8-hr, as Pb); NIOSH also targets blood-lead control"
      },
      "idlh": {
        "value": 100,
        "unit": "mg/m3"
      },
      "oshaStandard": "29 CFR 1910.1025 (general industry); 29 CFR 1926.62 (construction)",
      "filterNote": "Solid particulate and fume, non-oil - N/R/P all acceptable; N-series minimum. N100/P100 (100-series, HEPA-level) recommended given lead's toxicity and low PEL. Match respirator assigned protection factor to airborne Pb concentration.",
      "commonUses": "Storage-battery manufacture, radiation shielding, ammunition, soldering, leaded glass/crystal, legacy pigments and paint, smelting/secondary metal recovery, radiator repair, and demolition/renovation of lead-painted structures.",
      "notes": "Current IDLH is the revised value of 100 mg/m3 (as Pb); the original 700 mg/m3 and interim 400 mg/m3 figures are historical and no longer current. PEL and action level trigger medical surveillance and biological (blood-lead) monitoring under 1910.1025.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0368.html",
        "https://www.cdc.gov/niosh/idlh/7439921.html",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1025"
      ],
      "confidence": "high"
    },
    {
      "slug": "hexavalent-chromium",
      "name": "Hexavalent chromium (Cr(VI))",
      "particulate": true,
      "formula": "Cr(VI) (varies by compound; e.g., CrO3, chromates)",
      "casNumber": "18540-29-9 (chromium(VI) ion; individual Cr(VI) compounds have their own CAS)",
      "oshaPEL": {
        "value": 0.005,
        "unit": "mg/m3",
        "type": "8-hr TWA (as Cr(VI); 5 ug/m3); action level 0.0025 mg/m3"
      },
      "nioshREL": {
        "value": 0.0002,
        "unit": "mg/m3",
        "type": "TWA (0.2 ug/m3, as Cr(VI)); NIOSH Ca (potential occupational carcinogen)"
      },
      "idlh": {
        "value": 15,
        "unit": "mg/m3"
      },
      "oshaStandard": "29 CFR 1910.1026 (general industry); 29 CFR 1926.1126 (construction); 29 CFR 1915.1026 (shipyards)",
      "filterNote": "Present as dry dust/fume or as chromic-acid mist - use P100 as the robust default (P-series handles oil and non-oil mists/aerosols); N100 is acceptable for dry Cr(VI) particulate only. Carcinogen with a very low PEL, so HEPA-level (100-series) filtration and appropriate assigned protection factor are recommended.",
      "commonUses": "Chrome electroplating, welding of stainless and high-alloy steels (a major exposure source), chromate conversion coatings, chromate pigments and paints/primers, leather tanning, and legacy chromated-copper-arsenate wood preservation.",
      "notes": "IDLH of 15 mg/m3 (as Cr(VI)) is the NIOSH value for chromic acid and chromates. NIOSH REL (0.0002 mg/m3) is far below the OSHA PEL (0.005 mg/m3) because NIOSH treats all Cr(VI) compounds as occupational carcinogens.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0138.html",
        "https://www.cdc.gov/niosh/idlh/1333820.html",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1026"
      ],
      "confidence": "high"
    },
    {
      "slug": "cadmium",
      "name": "Cadmium",
      "particulate": true,
      "formula": "Cd",
      "casNumber": "7440-43-9",
      "oshaPEL": {
        "value": 0.005,
        "unit": "mg/m3",
        "type": "8-hr TWA (as Cd; 5 ug/m3); action level 0.0025 mg/m3"
      },
      "idlh": {
        "value": 9,
        "unit": "mg/m3"
      },
      "oshaStandard": "29 CFR 1910.1027 (general industry); 29 CFR 1926.1127 (construction)",
      "filterNote": "Solid particulate/fume, non-oil - N/R/P all acceptable; N100/P100 (HEPA-level) recommended because cadmium is a carcinogen with a very low PEL. Choose respirator assigned protection factor to the airborne Cd level.",
      "commonUses": "Nickel-cadmium batteries, electroplating and coatings, pigments, brazing/silver-solder alloys, PVC stabilizers, solar cells, and cadmium-bearing metal smelting/recovery.",
      "notes": "NIOSH does not assign a numeric REL: it recommends reducing exposures to the lowest feasible concentration and treats cadmium as a potential occupational carcinogen (Ca) - hence no nioshREL value is reported here. IDLH 9 mg/m3 applies to both cadmium dust and fume (as Cd).",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0087.html",
        "https://www.cdc.gov/niosh/idlh/7440439.html",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1027"
      ],
      "confidence": "high"
    },
    {
      "slug": "manganese",
      "name": "Manganese",
      "particulate": true,
      "formula": "Mn",
      "casNumber": "7439-96-5",
      "oshaPEL": {
        "value": 5,
        "unit": "mg/m3",
        "type": "Ceiling (C), as Mn (not a TWA - never to be exceeded)"
      },
      "nioshREL": {
        "value": 1,
        "unit": "mg/m3",
        "type": "TWA (as Mn); STEL 3 mg/m3"
      },
      "idlh": {
        "value": 500,
        "unit": "mg/m3"
      },
      "oshaStandard": "29 CFR 1910.1000 Table Z-1 (no substance-specific manganese standard)",
      "filterNote": "Fume and dust, non-oil - N-series acceptable; N95 minimum, with N100/P100 recommended for welding-generated Mn fume and higher concentrations. Because welding Mn often co-occurs with Cr(VI)/Ni, select the filter for the most protective constituent.",
      "commonUses": "Steel and ferroalloy production (ferromanganese), welding electrodes and consumables (a leading occupational exposure source, linked to manganism), dry-cell batteries, glass, ceramics, fertilizers and fungicides (e.g., maneb), and the MMT fuel additive.",
      "notes": "The OSHA limit is a CEILING of 5 mg/m3 (as Mn), not an 8-hr TWA - a distinction that matters for exposure comparisons. NIOSH is markedly lower (1 mg/m3 TWA, 3 mg/m3 STEL). No substance-specific OSHA standard exists; enforcement is under Table Z-1.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0379.html",
        "https://www.cdc.gov/niosh/idlh/7439965.html",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ],
      "confidence": "high"
    },
    {
      "slug": "wood-dust",
      "name": "Wood dust",
      "particulate": true,
      "formula": "— (cellulosic organic particulate; species-dependent)",
      "casNumber": "None (natural product; no single CAS)",
      "oshaPEL": {
        "value": 15,
        "unit": "mg/m3",
        "type": "8-hr TWA total dust (5 mg/m3 respirable) - enforced under Particulates Not Otherwise Regulated; there is NO wood-dust-specific OSHA PEL (the 1989 value was vacated in 1992)."
      },
      "nioshREL": {
        "value": 1,
        "unit": "mg/m3",
        "type": "TWA; NIOSH Ca (potential occupational carcinogen). Western red cedar limit is 0.5 mg/m3."
      },
      "oshaStandard": "29 CFR 1910.1000, Table Z-1 (enforced under the PNOR limits; no wood-dust-specific standard)",
      "filterNote": "Coarse-to-fine solid organic particulate, non-oil - N-series acceptable; N95 is generally adequate for nuisance loading. Upgrade to N100/P100 for hardwood dust (associated with sinonasal cancer) and for high dust concentrations or long durations.",
      "commonUses": "Sawmills, furniture and cabinet making, millwork, flooring, carpentry, pattern making, and general woodworking/construction operations such as sawing, sanding and routing.",
      "notes": "Current OSHA enforcement is via the PNOR limits (15 mg/m3 total / 5 mg/m3 respirable) because the wood-dust-specific 1989 PEL (5 mg/m3 TWA, 10 mg/m3 STEL) was vacated by the 11th Circuit in 1992. NIOSH is far lower (1 mg/m3, or 0.5 mg/m3 for Western red cedar) and classifies wood dust as a carcinogen (nasal cancer, chiefly hardwoods). No IDLH is established for wood dust.",
      "sources": [
        "https://www.cdc.gov/niosh/npg/npgd0667.html",
        "https://www.osha.gov/wood-dust/hazards",
        "https://www.osha.gov/annotated-pels/table-z-1"
      ],
      "confidence": "high"
    },
    {
      "slug": "particulates-not-otherwise-regulated",
      "name": "Particulates not otherwise regulated (PNOR)",
      "particulate": true,
      "formula": "— (catch-all for inert dusts without a specific standard)",
      "casNumber": "None (regulatory category, not a single substance)",
      "oshaPEL": {
        "value": 15,
        "unit": "mg/m3",
        "type": "8-hr TWA total dust; 5 mg/m3 8-hr TWA respirable fraction"
      },
      "oshaStandard": "29 CFR 1910.1000, Table Z-1 ('Particulates not otherwise regulated (total)' and 'respirable fraction')",
      "filterNote": "Solid nuisance particulate, non-oil - N-series is sufficient; N95 minimum. Upgrade to N100/P100 for high dust loading, comfort, or where the specific dust later proves to have a more hazardous constituent. Not a gas/vapor hazard, so no chemical cartridge is required.",
      "commonUses": "Default category for inert/nuisance mineral, inorganic and organic dusts lacking a specific PEL - e.g., limestone/calcium carbonate, marble, gypsum, cellulose, Portland-cement-type dusts, and many other bulk dusts.",
      "notes": "PNOR is a fallback for solid particulates that have no substance-specific standard; it is equivalent to the older 'inert or nuisance dust' limit. If a dust is later identified as a regulated substance (silica, lead, etc.), the substance-specific PEL supersedes PNOR. NIOSH does not publish a numeric REL for the PNOR category, and no IDLH is defined.",
      "sources": [
        "https://www.osha.gov/chemicaldata/801",
        "https://www.osha.gov/annotated-pels/table-z-1",
        "https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1000TABLEZ1"
      ],
      "confidence": "high"
    }
  ]
}