May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: 1321–64–8

NIOSH REL: 0.5 mg/m3 TWA [skin]

Current OSHA PEL: 0.5 mg/m3 TWA [skin]

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 0.5 mg/m3 TWA [skin]

Description of substance: Pale-yellow or white solid or powder with an aromatic odor.

LEL: . . Noncombustible Solid

Original (SCP) IDLH*: Unknown [*Note: Effective IDLH = 5 mg/m3 — see discussion below.]

Basis for original (SCP) IDLH: AIHA [1970] reported that the atmospheric concentration immediately hazardous to life is probably unattainable for the chloronaphthalenes with the possible exception of monochloronaphthalene. For this draft technical standard, however, an analogy with other chloronaphthalenes was used, and the respirators were selected on the basis of the assigned protection factor afforded by each device up to 10 ´ the OSHA PEL of 0.5 mg/m3 (i.e., 5 mg/m3); only the “most protective” respirators are permitted for use in concentrations exceeding 5 mg/m3.

Short-term exposure guidelines: None developed


Animal or human data: None relevant for use in determining the revised IDLH.

Revised IDLH: Unknown [Unchanged]

Basis for revised IDLH: Due to a lack of relevant acute toxicity data, the IDLH for pentachloronaphthalene remains "Unknown." The "most protective" respirators will continue to be recommended for concentrations exceeding 5 mg/m3 based on being 10 times the NIOSH REL and OSHA PEL of 0.5 mg/m3 (10 is an assigned protection factor for respirators and was used during the Standards Completion Program for deciding when the "most protective" respirators should be used for pentachloronaphthalene).


1. AIHA [1966]. Chloronaphthalenes. In: Hygienic guide series. Am Ind Hyg Assoc J 27:89-91.

Page last reviewed: December 4, 2014