The importance of a good quality fire blanket - Part 2
My previous blog on Fire Blankets covered the product and the standard BS EN 1869:1997. I’d like to expand a bit more on Clause 4 of the standard – Fire Performance, which is described in detail in Annex C.
The test resembles a ‘sanitized’ chip pan containing of 3 litres of cooking oil which is kept on a burner so that it ignites of its own accord (auto-ignition). The size, shape and design of the pan is standardized, together with the oil used and the conditions are controlled too, to ensure repeatability.The fire test is arguably the most critical part of the standard and for those of you who have witnessed this test know it can be quite dull, but with a few minutes of intense tension now and again!
The oil is heated by means of a gas burner at a steady rate so that the oil self-ignites within 25 to 35 minutes. The auto-ignition point should be between 350 ℃ to 370 ℃ and it is the last few degrees of heating that provide the most tension. I’ve been guilty of holding my breath at this point hoping that the oil ignites at the correct time and temperature so that the test can proceed.
As you may realize the oil type is critical and is currently “an edible cooking oil, free from additives” and two oils are noted in the current standard (Soya bean and Rapeseed oils). As an aside, walking through a supermarket with a trolley containing forty litres of cooking oil is an experience!
Once the oil ignites, the gas-burner is removed and simultaneously 2 minutes is started on the clock. These 2 minutes are to allow the fire to burn freely and allow the combustion products to escape. It is worth noting that the smoke produced is quite copious, it also taints everything with the smell of cooking oil!
Once the 2 minutes are completed, the fire blanket is deployed. This is the first appearance of the product under test, being used for what it was designed for. This again is a tense moment as the placement needs to be central to the pan, although some adjustment is permitted. There is then a 15-minute wait and the fire is considered extinguished if there are no visible flames and no reignition within 3 minutes of removal of the blanket.
The removal of the blanket is therefore another tense moment as the blanket could have insulated the pan not allowing the heat to dissipate, so that there is the possibility of a failure caused by reignition of the oil.
So, nearly an hour of “not much” with a few moments of high tension. It’s all important really, measured and timed with calibrated equipment and usually videoed for analysis later. The tests are also carried out as a set of three, so there are two more to complete before the blanket gets a “pass” for the fire performance clause.
Obviously, the tension is nothing compared to finding a real chip pan on fire, but hopefully the testing and certification will ensure that the product works when it is really needed!
As a Post-Script to this blog, the new version (BS EN 1869:2019) has now been issued with new fire tests (cooking oil fires and heptane fires) however I’m sure that the tension is still going to be there! I’ll blog on the new standard soon.
Author: Antony Field
Certification Manager - Fire, EMEA