Required delivered density (RDD)
When insurance companies underwrite risks, they depend on precise tests to evaluate whether existing sprinkler systems will control or suppress specific fire challenges. UL tests the combustion characteristics of a broad range of commodities in various packaged configurations (e.g., type of pallet used, corrugation, shrink wrap) and assigns a commodity hazard classification referenced in NFPA 13. UL's detailed reports give insurers all the information they need to assess risk fairly and accurately.
Large-scale testing equipment for precise measurements
UL conducts these tests in a 25-foot-diameter calorimeter hood designed to collect burning gases during flaming combustion. Its large-scale calorimeter can measure heat release rates of approximately 10 megawatts with an exhaust of 60,000 CFM. UL measures the total heat release rate using oxygen depletion principles. A fire model is used to determine when an automatic sprinkler would activate, given a real-time calculation of the heat release rate. This model uses the following parameters as part of the calculation:
- Sprinkler activation temperature
- Sprinkler response time index (RTI)
- Radial distance of sprinkler to center of fire
- Distance of ceiling to top of commodity
- Number of storage tiers
When the heat reaches the sprinkler activation point, UL uses full-cone pattern spray nozzles to apply water uniformly over the top of the burning commodity.
Test Standards
UL tests to the current editions of the following Standard:
- UL2335, Fire Tests of Storage Pallets
Flexible testing provides specific answers
UL fire tests classify commodities based on how they react under storage conditions:
- Commodity Classification - Classifies a product and its associated packaging system in a rack storage arrangement
- Pallet Classification - Measures the heat release contribution of storage pallets in a rack storage arrangement
The UL advantage
Hazard ratings depend on a number of factors, including product materials, packaging and the pallets used for shipping. UL engineers can work with manufacturers and packaging engineers to develop packaging and transportation solutions that provide safe transportation while reducing fire risk. Up-front planning can help manufacturers lower their commodity classification, while still meeting the requirements of their retail customers. Leading-edge equipment, engineering expertise, and more than 100 years of Standards development, testing and certifying experience make UL a valuable resource for product development and performance analysis.
