The Acceptable Solutions C/AS1 to the New Zealand Building Code impose a limit of 50 people that may be served by a single escape route. Restrictions are also placed on the travel distance between the most distant occupied space and the distance to reach the nearest safe path, safe place, or another firecell. These restrictions are related to the nature of the occupancy of the firecell, and the detection systems installed. This report compares the requirements of the New Zealand Acceptable Solutions with other equivalent documents from the United Kingdom and the United States of America, and assess the escape times associated with the requirements. It then reviews the detection, pre-movement, tenability, and available escape times from various standard t² and item fires in a variety of firecell sizes, for a variety of occupancies, and quantifies the probability of successful egress from an open plan firecell with a single means of escape. It is shown that if an adequate egress width is provided, the number of occupants in the room need not influence the time required to egress, but that the minimum door widths required by most approved documents will result in some queuing. Therefore, the limit of 50 people does not appear to result from a fire safety consideration, provided adequate egress widths are provided. It is concluded that the risk of obstruction by the fire is generally small, with the most likely cause of failure being from loss of tenability in the firecell. The greatest chance of successful egress is from a large firecell, there being few successful outcomes from small firecells. The provision of sprinklers has little effect on the tenability time in the firecell. There is some improvement in larger firecells, but not in those with smaller floor areas. The main benefit is in the control of the fire size, reducing the radiation levels and hence the risk of the fire obstructing the egress route.