The exposure to chemicals or ionizing radiation with hazardous effect on the human body. Solid and liquid toxic effects may be presented as LD₀, LD₁₀, or LD₅₀, describing the dose that will produce 0, 10 per cent or 50 per cent chance of fatality, respectively. The values are usually milligrams per kg body weight. Another form of dose is the OEL (Occupation Exposure Limits). The TLV is the Threshold Limit Value for eight hours per day, while the STEL is the Short Term Exposure time for fifteen minutes. For ionizing radiation, the dose is a measure of the extent to which the human body has been exposed. The absorbed dose is the amount of energy per unit mass. The SI unit is the gray or the rad where 1 rad = 0.01 gray. The dose rate is the exposure to ionizing radiation expressed as the ratio of dose with time.