Hafnium compounds (as Hf)

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
HfCl Rat	Izmerov et al. 1982	oral	2,362	-----	13,791 mg Hf/m3	1,379 mg Hf/m3
HfCl2O Mouse	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.