Hafnium compounds (as Hf)
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  stated that hafnium metal has a low order of toxicity. ILO  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|
|Izmerov et al. 1982||oral||2,362||—–||13,791 mg Hf/m3||1,379 mg Hf/m3|
|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/m3Basis 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.|
1. Haley TJ, Raymond K, Komesu N, Upham HC . The toxicologic and pharmacologic effects of hafnium salts. Toxicol Appl Pharmacol 4:238-246.
2. ILO . 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 . Toxicometric parameters of industrial toxic chemicals under single exposure. Moscow, Russia: Centre of International Projects, GKNT, p. 71.
4. MCA . 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.