The amount of the lump sum shall be determined as follows:

1. (a) If the injury causes temporary disability, the appeals board shall estimate the probable duration thereof and the probable amount of the temporary disability payments therefor, in accordance with Chapter 2 of Part 2 of this division, and shall fix the lump sum at the amount so determined.
2. (b) If the injury causes permanent disability or death, the appeals board shall fix the total amount of the permanent disability payment or death benefit payable therefor in accordance with Chapter 2 of Part 2 of this division, and shall estimate the present value thereof, assuming interest at the rate of 3 percent per annum and disregarding the probability of the beneficiary’s death in all cases except where the percentage of permanent disability is such as to entitle the beneficiary to a life pension, and then taking into consideration the probability of the beneficiary’s death only in estimating the present value of such life pension.