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Hafnium compounds (as Hf)																				Related Pages
										May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)
**CAS number:** 7440–58–6 (Metal)
**NIOSH REL:** 0.5 mg/m3 TWA
**Current OSHA PEL:** 0.5 mg/m3 TWA
**1989 OSHA PEL:** Same as current PEL
**1993-1994 ACGIH TLV:** 0.5 mg/m3 TWA
**Description of Substance:** Varies
**Original (SCP) IDLH*:** Unknown [*Note: “Effective” IDLH = 250 mg Hf/m3 — see discussion below.]
**Basis for original (SCP) IDLH:** MCA [1966] stated that hafnium metal has a low order of toxicity. ILO [1972] reported that hafnium compounds appear to have an acute toxicity slightly greater than those of corresponding zirconium salts (ZrCl4, ZrOCl2) [Haley et al. 1962]. However, respirators have been selected on the basis of the assigned protection factor afforded by each device up to 500 × the OSHA PEL of 0.5 mg/m3 (i.e., 250 mg/m3); only the “most protective” respirators are permitted for use in concentrations exceeding 250 mg/m3.
**Short-term exposure guidelines:** None developed
**ACUTE TOXICITY DATA**
**Lethal dose data:**

**Species**
    **Reference**
    **Route**
    **LD50** **(mg/kg)**
    **LDLo** **(mg/kg)**
    **Adjusted LD**
    **Derived value**HfClRat
    Izmerov et al. 1982
    oral
    2,362
    -----
    13,791 mg Hf/m3
    1,379 mg Hf/m3HfCl2OMouse
    Haley et al. 1962
    oral
    76
    -----
    359 mg Hf/m3
    36 mg Hf/m3
 **Human data:** None relevant for use in determining the revised IDLH.
 
 **Revised IDLH:** 50 mg Hf/m3**Basis for revised IDLH:** No inhalation toxicity data are available on which to base an IDLH for hafnium compounds. Therefore, the revised IDLH for hafnium compounds is 50 mg Hf/m3 based on acute oral toxicity data in animals [Haley et al. 1962]. This may be a conservative value due to the lack of acute inhalation toxicity data for workers.
**REFERENCES:**
1. Haley TJ, Raymond K, Komesu N, Upham HC [1962]. The toxicologic and pharmacologic effects of hafnium salts. Toxicol Appl Pharmacol *4*:238-246.
2. ILO [1972]. Zirconium, hafnium. In: Encyclopaedia of occupational health and safety. 2nd ed. Vol. II (L-Z). Geneva, Switzerland: International Labour Office, pp. 1528-1529.
3. Izmerov NF, Sanotsky IV, Sidorov KK [1982]. Toxicometric parameters of industrial toxic chemicals under single exposure. Moscow, Russia: Centre of International Projects, GKNT, p. 71.
4. MCA [1966]. Chemical safety data sheet SD-92: properties and essential information for safe handling and use of zirconium and hafnium powder. Washington, DC: Manufacturing Chemists Association, Inc., pp. 1-10.

			
							
								Page last reviewed:  December 4, 2014						Content
							source: 	National Institute for Occupational Safety and Health NIOSH Publications & Products
Immediately Dangerous To Life or Health (IDLH) Values
Table of IDLH Values
Criteria for Determining IDLH Values
Historical Documentation
Original (SCP) Values
Abbreviations for IDLH Documentation
Abbreviations for Journal Titles Follow NIOSH Facebook
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