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Table 3 Summary of exposure regulation and guideline levels for TDI, MDI and HDI. This table includes the lethal dose 50 (LC50) for rats in ppm as well as the short term and long term levels for the respective airborne isocyanate from regulating organs

From: The role of isocyanates in fire toxicity

Compound Agency LC50a (ppm) Short term exposure Long term exposure
    STEL (ppm) AEGL1 (ppm) AEGL2 (ppm) AEGL3 (ppm) ERPG2 (ppm) ERPG3 (ppm) TWA (ppm) REL (ppm)
TDI (Both isomers)   14   10 min 30 min 10 min 30 min 10 min 30 min     
  OSHA   0.2       0.005  
  UK HSE   0.041b       0.0116b  
  US EPA    0.02 0.02 0.24 0.17   0.65     
  NIOSH          0.005 (TWA), 0.02c
  ACGIH   0.02       0.005  
  AIHA       0.15 0.6   
MDI   36         
  OSHA   0.2       0.005  
  UK HSE   0.04b       0.0116b  
  US EPA    N/A N/A N/A N/A N/A N/A    0.65  
  NIOSH          0.005 (TWA), 0.02c
  ACGIH   0.02       0.005  
  AIHA       0.5 5.4   
HDI   22         
  OSHA   N/A        
  UK HSE   0.04b       0.0116b  
  US EPA    N/A N/A N/A N/A N/A N/A     
  NIOSH          0.005 (TWA), 0.02c
  ACGIH         0.005  
  AIHA       N/A N/A   
  1. aRat inhalation (4 h)
  2. bAs NCO-group
  3. cTen minute exposure
  4. STEL Short-term exposure limit (15 min unless otherwise stated), AEGL1 Acute Exposure Guideline Level 1 “Notable discomfort, irritation, or certain asymptomatic non-sensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure”, AEGL2 Acute Exposure Guideline Level 2 “Irreversible or other serious, long lasting adverse health effects or an impaired ability to escape”, AEGL3 Acute Exposure Guideline Level 3 “Life threatening health effects or death”, ERPG2 Emergency Response Planning Guidelines level 2 “is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 h without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action”, ERPG3 Emergency Response Planning Guidelines level 3 “the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 h without experiencing or developing life-threatening health effects”, TWA Time weighted average (8 h per day during 40 h week unless otherwise stated), REL Recommended exposure limits
  5. N/A indicates level not available/not applicable