Read part 1 here.
Standards of fire resistance
When choosing a fire resistant conveyor belt, establishing the correct level or standard of fire resistance needed for a specific application or environment is of crucial importance. This can present one of the most difficult challenges for users of conveyor belts. For the vast majority of belts being used in the open air, Class 2A or 2B would be perfectly adequate. Class 2A demands that the belt is able to pass the ISO 340 test, described above, with the covers intact on the belt samples (K grade). Class 2B requires that the belt can also pass the ISO 340 test with the top and bottom cover rubber removed (S grade). As mentioned previously, the electrical conductivity of the belt also needs to fulfill the requirements of ISO 284.
If there is still uncertainty regarding the fire resistant grade of belting needed then it is best to carry out an internal risk assessment. If the expertise for this does not exist within the company then there are a number of external organisations (and almost certainly insurers) that can perform this function.
For conveyors carrying materials that contain oil such as wood chips and biomass (some types can spontaneously combust), rubber compounds that are resistant to fire, abrasion and oil are available. There are, of course, two types of oil resistance – mineral and vegetable. This is yet another important consideration when deciding on the correct type of fire resistant belt, so buyers are recommended to be very specific when making requests for quotations from manufacturers and suppliers.
DIN 22118 test at Dunlop.
CEN fire test standards
One of the most problematic aspects of fire testing rubber conveyor belts for industrial use above ground is that most of the test methods were established many years ago specifically for underground mining belts. Enormously complex and very costly testing has to be made by independent testing institutions. As a result of environmental regulations, large scale gallery fire tests now involve using a 12 m long container filled with carbon to filter the smoke emissions before being released into the atmosphere. In order to be awarded a safety standard certificate, every belt type has to be independently tested. For some tests a minimum of 20 m of belt is needed.
Such tests can easily cost up to €20 000 or more. For the manufacturers of solid woven underground mining belts and steelcord belting this is not a particularly big problem because there are a relatively small number of different belt types that have to be supplied for testing in large quantities. Although the test certificates are valid for several years, these large scale tests present a huge and costly problem to manufacturers of rubber belting for above ground use because there is a much wider range of belt types. Such complex test methods have made it extremely difficult to develop improved levels of fire safety because if a belt sample fails the tests then the technicians have to go back to the drawing board to make further changes to the rubber compound and then embark on another round of expensive tests.
Apart from hindering development of fire resistant belting, it also means that it is difficult to adequately test those belts that manufacturers claim reach specific levels of fire resistance. This is one of the reasons why there are so many end-users operating conveyors fitted with belts that provide inadequate levels of fire safety.
Conveyors can spread fire very quickly.
New CEN fire test standards to be introduced
This problem has long been recognised by the European Committee for Standardization (CEN) and over the last few years they have been trying to find a solution. Following recent meetings attended by technical experts from all over Europe, the CEN standards committee will introduce several positive changes in 2014.
Agreement has been reached on using and adapting tests already in existence for quality standards such as DIN and BS that will involve smaller scale tests using much smaller equipment. This will mean that major manufacturers will be able to experiment and carry out testing in their own laboratories. Ironically, these new test methods will actually be even more demanding than the old, large scale tests. Major insurance companies are already showing interest and are becoming involved in discussions. For them, and for all genuinely safety conscious organisations, this can only be very good news.
Don’t play with fire
Although manufacturers and suppliers may be able to provide test certificates, in some cases the certificate may only relate to the belting that the manufacturer produced for test certification purposes. In reality, the actual belt delivered to site may well not be up to the required standard. For greater peace of mind, Dunlop would suggest ordering an extra metre of belt and then have that piece of belt tested by an accredited testing authority or laboratory.
The price of not exercising caution simply cannot be calculated.
Written by Sytze Brouwers, Fenner Dunlop BV (Dunlop Conveyor Belting), The Netherlands. Sytze Brouwers is Chairman of the International Standards (ISO and CEN) committee and one of the world’s leading authorities on conveyor belting.
This is an abridged version of the full article, which appeared in the 2014 Bulk Materials Handling Review supplement of World Cement. Subscribers can view the full article by logging in.
Read the article online at: https://www.worldcement.com/europe-cis/04092014/playing-with-fire-part-2/