adult spends 1/4th of his or her time sitting on furniture upholstery treated with antimony trioxide, that 1/4th of the upper torso is in contact with the upholstery, and that clothing presents no barrier. Antimony trioxide is considered to be ionic, and is essentially not absorbed through the skin. However, to be conservative, the subcommittee assumed that ionized antimony trioxide permeates the skin at the same rate as water, with a permeability rate of 10⁻³ cm/hr (EPA 1992). Using that permeability rate, the highest expected application rate for antimony trioxide (2.5 mg/cm²), and Equation 1 in Chapter 3, the subcommittee calculated a dermal exposure level of 2.0×10⁻² mg/kg-d. The oral RfD for antimony trioxide (0.2 mg/kg-d; see Oral RfD in Quantitative Toxicity section) was used as the best estimate of the internal dose for dermal exposure. Dividing the exposure level by the oral RfD yields a hazard index of 0.1. Thus it was concluded that antimony trioxide used as a flame retardant in upholstery fabric is not likely to pose a noncancer risk by the dermal route.

The assessment of the noncancer risk by the inhalation route of exposure is based on the scenario described Chapter 3. This scenario corresponds to a person spending 1/4th of his or her life in a room with low air-change rate