Page:NIOSH Manual of Analytical Methods - Chapter K.pdf/5

 The primary sources of exposure criteria for workplace inhalation exposures are the following: (1) NIOSH recommended exposure limits (RELs),42 (2) the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs®),43 and (3) the U.S. Department of Labor, OSHA permissible exposure limits (PELs).44 These exposure criteria are for diisocyanate monomers. In July 1992, the 11th Circuit Court of Appeals vacated the 1989 OSHA PEL Air Contaminants Standard. OSHA is currently enforcing the 1971 standards which are listed as transitional values in the current Code of Federal Regulations; however, some states operating their own OSHA approved job safety and health programs can have lower limits. Table 1 contains a comparison of the respective NIOSH RELs, ACGIH TLVs, OSHA PELs, and United Kingdom Health and Safety Executive (UK-HSE) exposure criteria for the isocyanates. The UK-HSE has taken a different approach, i.e., developing a non-specific standard based on the total number of reactive isocyanate groups (TRIG) in a volume of air.45 The standards and limits listed in Table 1 are based on a general standard that isocyanate exposures should not exceed an 8-hour time-weighted average (TWA) exposure of 5 parts per billion (ppb), or a short term or ceiling exposure of 20 ppb.

Table 1: NIOSH, ACGIH, OSHA, and UK-HSE Exposure Criteria for Isocyanates Isocyanate Species

1

2

Exposure Criteria - Full-shift TWAs Micrograms per cubic meter of air

Exposure Criteria - Short Term or Ceiling Limits Micrograms per cubic meter of air

NIOSH REL

ACGIH TLV

UK-HSE

NIOSH REL Ceiling

ACGIH TLV-STEL

UK-HSE Ceiling

OSHA PEL Ceiling

TDI

CA-LFC1

36

None

None

140

None

140

MDI

50

51

None

200

None

None

200

HDI

35

34

None

140

None

None

None

HMDI

None

54

None

210

None

None

None

IPDI

45

45

None

180

None

None

None

NDI

40

None

None

170

None

None

None

TRIG2

None

None

20

None

None

70

None

NIOSH considers TDI to be an occupational carcinogen (CA) and recommends that exposures be reduced to the lowest feasible concentration (LFC). TRIG - total reactive isocyanate group.

Table II. Comparison of NIOSH and OSHA Isocyanate Methods NIOSH 5521

NIOSH 5522

NIOSH 2535

OSHA 42/47

PROPOSED NEW NIOSH1

a) Monomers

TDI, MDI, HDI, NDI, HMDI2

TDI, MDI, HDI, NDI, HMDI,2 IPDI 2

TDI, HDI

42 TDI, HDI 47 MDI

TDI, HDI, MDI, NDI,2 HMDI,2 IPDI 2

b) Oligomers

HDI

TDI, MDI, HDI

None

None

HDI, MDI,2 TDI2

impinger

impinger

coated glass wool/opaque tube

coated GFF

impinger; GFF; impinger+GFF

Isocyanate

Sampler

1/15/98

119

NIOSH Manual of Analytical Methods