A Guide to Fire Retardant Conveyor Belts

Bulk Handling of Fire Resistant Conveyor Belt Grades

EN Category 1. The EN standards outline the electrical and fire safety requirements for general purpose conveyor systems used above ground. Category 1 represents the basic classification, which requires the belt to be anti-static. This certification is necessary for use in ATEX 114 (Directive /34/EU) classified zones, if applicable.

Application: In settings where coal dust, fertilizers, grains, or other combustible materials like biomass are present, it is critical for the conveyor belt to not generate static electricity that could ignite the atmosphere. The belt should provide a pathway to ground for static electricity through the conveyor's metal framework instead of allowing it to build up. Thus, the safest practice is to ensure all belts adhere to EN Category 1.

EN Class 2A and Class 2B

The majority of tests concerning the fire resistance of belts are based on EN ISO 340*. These standards distinguish between fire resistance with covers, referred to as Class 2A (or K grade), and fire resistance with and without covers, categorized as Class 2B (or S grade). The importance of 'with and without covers' relates to the rubber skim layers nestled between synthetic plies, which protect the most flammable components in the belt's structure and provide a pathway for flames to spread. Therefore, the rubber skim material must exhibit fire resistance comparable to the outside covers. Unfortunately, manufacturers often compromise by using substandard rubber skims that lack adequate fire resistance or are excessively thin.

EN ISO 340 testing entails exposing six individual belt samples to an open flame, after which the flame source is removed. The duration of combustion is noted, followed by the application of air current to check for reignition. The ideal self-extinguishing time post-flame removal should be below 15 seconds for each sample and a cumulative maximum of 45 seconds across all tests. This average time should not exceed 7.5 seconds. This factor is essential as it influences how far a fire can advance along a moving belt. Consequently, Fenner Dunlop in The Netherlands aims for a maximum average of only one second—more than six times faster than the required standard.

Application: For most bulk material handling operations conducted outdoors, EN Class 2A (K grade) or Class 2B (S grade) fire resistance levels are generally sufficient. Determining the choice between Class 2A and Class 2B depends on the type of material being transported. Moderately abrasive substances like grain typically find Class 2A sufficient. However, for more abrasive materials that wear down the top cover quickly or require a higher fire safety level, opting for Class 2B is advisable.

EN Class 4A

Class 4A necessitates a more rigorous fire testing in accordance with EN -1 methods A, C, or D, in addition to EN ISO 340 testing.

Application: This heightened level of fire safety is particularly vital when conveying biomass since the dry, flammable dust produced can ignite from static electricity generated by friction within the conveyor system, with ignition requiring as little as 17mJ of energy. Additionally, biomass dust is susceptible to auto-ignition, especially when damp, potentially leading to self-heating and the release of gases such as carbon dioxide, carbon monoxide, and methane.

While using covered conveyors helps reduce this risk, enclosed settings pose an increased threat to human safety as burning rubber belts generate thick, toxic smoke that consists of cyanide, carbon monoxide, sulfur dioxide, and byproducts of butadiene and styrene. Consequently, EN Class 4A is typically the best option for conveyors operating in confined or covered areas.

Safety Is Priceless

Experience unequivocally illustrates that the price of conveyor belts directly correlates with their overall performance, including their ability to extinguish fires in a timely manner. While low prices may be alluring, it is crucial to understand how these cost reductions occur. The primary reason is that raw materials, particularly the expensive chemicals used in producing rubber with superior fire resistance standards, account for up to 70% of a conveyor belt's production costs. Therefore, to manufacture a low-priced belt, manufacturers often resort to using inferior raw materials or omitting essential additives. The price of a conveyor belt lacking sufficient fire-resistance cannot be quantified; it is fundamentally a matter of safety and survival.

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