Boron oxide

CAS number. . . . . . . . . . .  1303-86-2
NIOSH REL . . . . . . . . . . .  10 mg/m3 TWA
Current OSHA PEL. . . . . . . .  15 mg/m3 TWA
1989 OSHA PEL . . . . . . . . .  10 mg/m3 TWA
1993-1994 ACGIH TLV . . . . . .  10 mg/m3 TWA
Description of Substance. . . .  Colorless, semitransparent lumps or hard,
                                 white, odorless crystals.
LEL . . . . . . . . . . . . . .  Noncombustible Solid
Original (SCP) IDLH*. . . . . .  No Evidence [*Note:  "Effective" IDLH = 7,500
                                 mg/m3 -- see discussion below.]
Basis for original (SCP) IDLH .  No evidence exists in the available
                                 toxicological data that an acute exposure to
                                 a high concentration of boron oxide would
                                 impede escape or cause any irreversible
                                 health effects within 30 minutes.  For this
                                 draft technical standard, therefore,
                                 respirators have been selected on the basis
                                 of the assigned protection factor afforded by
                                 each device.  However, for some particulate
                                 substances for which no evidence of an IDLH
                                 exists, the determination of allowable
                                 respiratory protection based on protection
                                 factors may result in the assignment of
                                 respirators for concentrations that are not
                                 likely to be encountered in the occupational
                                 environment.  Therefore, for all such
                                 particulate substances it has been
                                 arbitrarily determined that only the "most
                                 protective" respirators are permitted for use
                                 in concentrations exceeding 500 x the OSHA
                                 PEL; in the case of boron oxide, 500 x the
                                 OSHA PEL of 15 mg/m3 is 7,500 mg/m3.
Short-term exposure guidelines.  None developed

ACUTE TOXICITY DATA

Lethal dose data:

                                                                              
                                     LL50    LDLo                    Derived
Species    Reference          Route (mg/kg) (mg/kg)   Adjusted LD     Value
______________________________________________________________________________
Mouse   Izmerov et al. 19825  oral   3,163   -----   22,141 mg/m3  2,214 mg/m3

Other animal data . . . . . . .  Rats exposed for 6 hours/day, 5 days/week for
                                 10 weeks to a concentration of 470 mg/m3
                                 showed no signs of intoxication other than
                                 mild nasal irritation [Wilding et al. 1959].
Human data. . . . . . . . . . .  None relevant for use in determining the
                                 revised IDLH.

Revised IDLH: 2,000 mg/m3
Basis for revised IDLH: The revised IDLH for boron oxide is 2,000 mg/m3 based on acute toxicity data in animals [Izmerov et al. 1982; Wilding et al. 1959].

REFERENCES:

1. Izmerov NF, Sanotsky IV, Sidorov KK [1982]. Toxicometric parameters of industrial toxic chemicals under single exposure. Moscow, Russia: Centre of International Projects, GKNT, p. 27.
2. Wilding JL, Smith WJ, Yevich P, Sicks ME, Ryan SG, Punte CL [1959]. The toxicity of boron oxide. Am Ind Hyg Assoc J 20:284-289.