2022-11-13
All materials, components, assemblies, products, and accessories referred to the UAE Fire and Life Safety Code shall be listed, approved, and registered by the Civil Defence (CD) Material Approval Department. The code has provisions for acceptable test standards and the criteria to follow. However, how do manufacturers, designers, and consultants choose the most appropriate prescribed method from the allowed standards to prove the fire safety compliance of construction materials, specifically interior finishes?
For the past years, numerous significant fire incidents have started with the ignition of interior finish from the walls, ceilings, or floors, as these products are often made of highly combustible synthetic materials. People lost their lives because of the dangers of harmful combustion gasses, room flashovers, and the limited time they had to get to safety.
Flashover, also known as rapid fire progress, is defined by NFPA 921 as "A transitional phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach its ignition temperature more or less simultaneously and fire spreads rapidly throughout the space resulting in full room involvement or total involvement of the compartment or enclosed area." The UAE CD regulates testing for interior finishes to verify that every combustible surface exposed to thermal radiation in a compartment or enclosed space does not rapidly and simultaneously ignite and results in a flashover.
One accepted fire test method for internal finishes is ASTM E84/UL 723, of which the apparatus is commonly known as the Steiner tunnel. It is a 10-min fire -test response method used to determine the burning behaviour of the material by observing the flame spread along the specimen and the smoke developed. The test is conducted with the sample placed in the ceiling position of the apparatus with the exposed surface to be evaluated face down to the ignition source. Yet is the flame spread and smoke developed index adequate to assess the fire safety of all types of interior finishes?
Research by Babrauskas(A), without bias on the European standards, showed that some materials with values of Class A and B tested in the Steiner tunnel, following the classes per their flame spread and smoke-developed indexes in the International Building Code 2018, Section 803.1.2, resulted to a flashover in less than 5 minutes. A lower flame spread index does not reliably increase the time to flashover.
In due consideration, the standard has mentioned, nevertheless, that not all materials can be tested in the Steiner tunnel:
“Testing of materials that melt, drip, or delaminate to such a degree that the continuity of the flame front is destroyed, results in low flame spread indices that do not relate directly to indices obtained by the testing materials that remain in place.”
With this, if the Steiner tunnel results do not correlate with some materials' flashover potential, who will determine if this test method is inappropriate for a particular product type?
According to studies by Underwriters Laboratories (UL)(B), the flashover rate for modern homes is eight times faster than it was 50 years ago; before, the average time it took a home fire to transition to a flashover was over 29 minutes. Underwriters Laboratory (UL) determined that fires today are more dangerous and pose more risks than in the past. Fire propagation is said to be faster, and time to flashover, escape times and collapse times are shorter.
By then, in these evolving times, what can be considered a measurement technique to assess the combustibility of materials?
Along with ASTM E84/UL 723, UAE Fire and Life Safety Code acceptable methods also include EN Standards (EN); ENs are documents ratified by one of the three European Standardization Organisations (ESOs), CEN, CENELEC or ETSI.
The European standard revolves around the EN 13823 or Single Burning Item test, an intermediate-scale test method to measure heat and smoke release rate, lateral flame spread and flaming droplets. Heat release rate relates to the amount of energy generated during combustion and plays on the oxygen consumption principle, which shows that the heat released from a burning specimen is directly related to the oxygen consumed during that combustion.
Research by Babrauskas and Peacock©, “Heat release rate: The single most important variable in fire hazard”, illustrated that even though toxic gases primarily cause fire deaths, the heat release rate is the best predictor of fire performance. The heat release rate is an influential parameter in characterising the “combustibility” of products and their fire hazard. Also, it can be used to evaluate different façade mock-ups (D).
During recent years, test equipment and procedures have become more available to express fire impact in a quantitative term. Consequently, the consultant should consider very carefully which method to use to measure the safety level of a product.
We at ESL believe that modern test equipment using heat release methods as a scientific approach heavily influences assessing a material’s behaviour during a real-fire scenario. Our team of experts can help consultants determine the proper selection of the most suitable method to ensure fire safety. Yes, we are here to help!
(A) https://dcat.net/~dcatnet/about_dcat/Babrauskas-et-al-2012(2).pdf
(B) https://www.montgomerycountymd.gov/frs-ql/Resources/Files/Accreditation/Accreditation_SOC_Reference_Files/2014_UL_Modern_Residential_Fires_Fact_Sheet.pdf
(C) https://www.sciencedirect.com/science/article/abs/pii/0379711292900199
(D) https://onlinelibrary.wiley.com/doi/full/10.1002/fam.2635