Like all precast, prestressed concrete products, hollowcore slabs have excellent fire resistance. Depending on thickness and strand cover, ratings up to a 4-hour endurance can be achieved. A fire rating is dependent on equivalent thickness for heat transmission, cover over the prestressing strand for strength in a high temperature condition and end restraint. Underwriters Laboratory (UL) publishes fire ratings for various assemblies. The fire ratings should be considered in determining the slab thickness to be used in preliminary design.
A typical 8-inch thick hollowcore plank has a 2-hour fire rating. For a higher rating (3- or 4- hour), typically a concrete (or gypsum based) topping would be applied or a spray-on fire resistant material can be added to the underside of the plank. This is also shown in the UL directory.
Model codes like the IBC have prescriptive fire ratings. This is the best way to indicate ways to accomplish specified fire ratings and should be the first choice. UL listings are another way to indicate how to achieve the specified fire ratings. The code does not require that UL listings be provided. These listings are the result of proprietary tests on specific precast units produced and tested by specific companies. If UL labels or numbers are required then the specific details in the UL Directory are exactly and only what will meet this requirement.
The PCI manual Design for Fire Resistance of Precast Prestressed Concrete illustrates the code accepted practice of rational fire design for precast and prestressed concrete products. In the case of hollowcore, an equivalent thickness is calculated based on the cross-sectional properties of each brand of hollowcore. Rational fire design is used for situations not covered by the code.
The Engineer-of-Record will decide if the floor slabs can be considered restrained or un-restrained. Tables in ASTM E119 discuss the restraint conditions and are also shown in the PCI Hollowcore Design Manual. Required fire ratings should be clearly specified in the contract documents.