Hello slate people
In recent years, I´ve heard more than once that question. Well, I think it is common knowledge for all of us that slate, as most of the rocks, does not burn, or neither release any hazardous substance when exposed to fire. So, why this question is in the spotlight? Due to the increase of gigantic, violent fire events we are experiencing as a result of the global warming (or climatic change), authorities, architects and general public are paying very much attention on the response to fire of the materials used in construction. We have seen entire towns completely reduced to ashes in California, and unfortunately, in the following years this is very much likely to be repeated. So this concern is fully justified. Till now, some companies and the National Slate Association have commissioned test to different testing materials laboratories. However, since the is no a specific standard for roofing slates, results have a certain margin of uncertainty which could be used in a hypothetical legal trial. Do not miss out that, in the worst scenario, insurance companies would appeal anything in order not to take charge of a possible compensation…even that the roofing slate installed was responsible of the fire. Therefore, we need absolute evidence that cannot be discussed.
Nowadays, science is communicated through the scientific journals which are indexed in a database named Web of Science. All papers published in these journals are subjected to peer review, which assures that other scientist from the same field of knowledge review and detect any incongruity in the papers. Therefore, papers published in these journals are accepted as scientific evidences. Taking into account the possible legal implications, and knowing that this work should be clear and undeniable, other colleagues and me performed a set of scientific tests on different types of roofing slates. In other words, we submitted slates to temperatures up to 900 °C (or 1650 °F if you prefer) and observed what happened. Not so much, really. All slates became reddish, as expected, since fire is one of the most powerful oxidant processes we know, and the bending strength diminished, they became more brittle. This result was also expected. Besides, we monitored the mineralogical and chemical changes held during fire exposure. Tests were held at the Universities of Ghent, Belgium, and Oviedo, Spain. Nothing more happened besides these two effects, color change and loss of mechanical resistance. No hazardous gases, nor the release of any damaging substance, and of course, none of the samples burned. They all just got very hot. We could have continued the test until melting of the slates, but nothing else would have happened. Slate does not burn. You can tell it to the insurance company. Check it by yourself, the paper is available at