To supersede the requirements of Sentence 3.2.3.19.(1) and require an increased minimum fire-resistance rating of 1 h [as opposed to 45 min] for the separation of buildings connected by underground walkways, on the basis that underground walkways pose greater difficulties to emergency responders [e.g. result in delays and ineffectiveness in fire suppression operations]. This increased minimum fire-resistance rating is to limit the probability of the spread of fire from one building to the adjacent building connected by means of the walkway, which could lead to damage to the connected building.