How do our fire prevention tests compare to industry standards?
Large-scale fire tests of oxygen-reduction systems by FM Global have shown their effectiveness but the results come with a note of caution, writes Jose Sanchez.
The results in the report published in January by FM Global are at odds with the oxygen levels that are stipulated by some international standards.
ORSs are fire prevention systems that are designed to create an environment that does not support ignition and propagation of fire. It does this by limiting the concentration of oxygen in a protected space, usually through the introduction of nitrogen. As the technology has evolved over the last ten years, so have related standards including EN 16750 that was published in September last year, and VdS 3527 that was last revised in 2015.
FM Global carried out the large-scale tests because the results of previous small-scale tests had been markedly different to industry-accepted standards. The point of difference is the limiting oxygen concentration (LOC), which is defined as the lowest O2 concentration that can support combustion for a given fuel. “One standard that was at the time of the tests, VdS 3527, which is available internationally to determine this minimum oxygen concentration, appeared quite high to us at more than 15%. Our own tests of 2007 had already looked into the situation and found that the concentration was significantly lower. We wanted to understand what should be the actual concentration,” says Sergey Dorofeev, vice president research area director, FM Global, who was responsible for the report.
The latest tests were designed to simulate current ORS applications in engineering practice as closely as possible. Five standard commodities were tested, arranged in rack storage. A constant mix of nitrogen/air was flowed in, with oxygen concentration rising in 2% steps from 9% to 17%. A premixed flame was used as an ignition source, replicating a heat source from electric arc or hot work, and therefore not sensitive to oxygen levels. “We looked at a variety of ignition sources that are typical of what we have in an insured location such as a warehouse, which is either electrical, hot work or arson. According to our statistical analysis the percentage of open flame ignition was very low. The type of energy of this ignition source is standard for other protection systems such as water mist or sprinklers and we want the protection level for all our systems at the same level,” explains Dorofeev.
The LOC for fire propagation was obtained for each of the five class of commodities, both with and without a sustained igniter. For cartoned Class 3, cartoned unexpanded plastic and cartoned expanded plastic, the LOC was 11.1% with a sustained ignition. The LOC from VdS’ standard was 15% for the same material. For plastics, the LOC was found by FM Global to be 13%, compared to VdS’ 15.9%.
The LOCs obtained by FM Global were generally lower than the O2 concentrations recommended by the VdS standard, but closely match FM’s previous small-scale tests. Why the two organisations should have such different results, suggests Dorofeev, may be down to the different configurations of arrays.
VdS has a vertical piece of a tested material that is open to heat losses due to radiation, which prevents ignition and flame spread. In FM Global’s tests, the pieces of tested material are facing each other through a narrow flue, which helps to trap radiation in the flue and facilitates ignition and flame spread. In addition, larger dimensions of the tested samples in FM Global’s tests facilitate ignition and flame spread.
As a result of the tests, Dorofeev says he is optimistic about this relatively new fire protection technology, but cautiously so. Firstly, because of the crucial need for maintaining oxygen concentration sufficiently low as to avoid flame spread. “Secondly, we need to understand the reliability and functionality of the system. We need to understand if we can rely on it in the same way as other protection systems that are out there, such as water mist, sprinklers and gaseous protection systems. That analysis is yet to be carried out.” A whole variety of aspects need to be considered, he adds, such as potential room openings, oxygen level sensors, suitable alarm system, and that personnel entering the room are trained to enter oxygen-depleted spaces. “If all these elements come together then I’m happy that it will be a good option for
protection,” he says.
Asked whether the test results may discourage companies from taking up the technology, Dorofeev recognises that the levels of oxygen required for fire protection point to its use in unoccupied spaces only. “Maybe it would be of interest to customers that have valuable storage that they want to protect from water damage. Or unoccupied machinery that is in a closed envelope and not normally attended by anyone. We like to have options for clients to choose the best method of fire protection.”
Looking to the future, Dorofeev estimates that that the first FM-approved oxygen-reduction system may be introduced in the next two years or so.
This article first appeared in Industrial Fire Journal. Click here to read.