This report covers the effect of safety factors on the time taken for humans to escape a building where fire has initiated. Monte Carlo simulation is used to determine the probability of failure to escape in a given fire scenario. The simulations indicate that the safety factor is very influential upon the probability of failure to escape. The major effects upon egress are ranked in this order of significance; time taken for the occupant to decide to leave the building after hearing the alarm, the time until conditions are too hostile for human survival, and the time until the fire is detected. The occupant's travel speed to leave the building has such a low level of significance that it should be treated deterministically in future studies of this type. Where a safety factor of two is applied there is a reasonable probability of failure.