The Importance of Auto Ignition Temperatures in ATEX Fan Selection
ATEX protection is all centred around preventing an explosion from happening when there is a presence of combustible dust or flammable gas, this means considering all potential ignition sources. When looking at sources, most people will look for sparks and flames as an obvious risk, but the gas or dust properties themselves are an important aspect to protect against.
One of these properties is their temperature characteristics. Flammable gases have specific ignition temperatures, known as autoignition temperatures. These temperatures represent the minimum temperatures at which a gas mixture will spontaneously ignite in the absence of an external ignition source such as a spark or a flame. As an example, the auto ignition temperature of hydrogen air or hydrogen-oxygen, is from 510 – around 584°C.
Let’s consider the principle of hot surface ignition – lots of processes, such as combustion, will utilise a gases auto ignition temperature to ignite a gas on contact with a hot surface (often a coil, thread, plate etc). This works as the high temperature of the surface transfers heat to the gas, raises the temperature to its auto ignition point, igniting, and sustaining combustion. Great for purposeful processes but when this is not considered when handling potentially hazardous gases, this can be the cause for the explosion.
The principle of hot surface ignition, and the avoidance of auto ignition is handled with surface temperature limitations. ATEX fan selections consider the maximum allowable surface temperature of fan motors that come into contact with these potentially flammable gases and dusts in hazardous ATEX environments. This concept is known as maximum surface temperature. It’s important to note that maximum temperature limitations are not in place primarily for the prevention of hot surface ignition, the main principle is to protect the motor components themselves to ensure their safe operation by preventing excessive heat build-up, but will also prevent the fan and motor from becoming a source of potential ignition by keeping temperatures below any auto ignition temperatures.
For those of you who are unfamiliar with the make-up of an industrial fan suitable for potentially hazardous environments, ATEX fans are constructed and classified in two parts, one label that explains the motor classification and protection, and secondly a rating for the overall fan construction including the casing, impeller, and materials. Part of the motor classification shows the end user the maximum surface temperature that the motor is limited to reach to prevent component getting so hot that it initiates the auto-ignition temperature of the surrounding flammable substances.
Your fan supplier should always ask for your hazardous area classification information, this will inform them of the gases or dusts present, their presence to determine the ATEX zone, the temperature limitations that must be considered, the materials required to ensure longevity and safe operation and the level of ATEX protection required from electrical components such as motors. Under DSEAR and ATEX legislation it is the sole responsibility of the end user to conduct or contract a hazardous area classification. Suppliers will not be able to supply equipment for hazardous areas without this information from the end users.
Let’s consider the principle of hot surface ignition – lots of processes, such as combustion, will utilise a gases auto ignition temperature to ignite a gas on contact with a hot surface (often a coil, thread, plate etc). This works as the high temperature of the surface transfers heat to the gas, raises the temperature to its auto ignition point, igniting, and sustaining combustion. Great for purposeful processes but when this is not considered when handling potentially hazardous gases, this can be the cause for the explosion.
The principle of hot surface ignition, and the avoidance of auto ignition is handled with surface temperature limitations. ATEX fan selections consider the maximum allowable surface temperature of fan motors that come into contact with these potentially flammable gases and dusts in hazardous ATEX environments. This concept is known as maximum surface temperature. It’s important to note that maximum temperature limitations are not in place primarily for the prevention of hot surface ignition, the main principle is to protect the motor components themselves to ensure their safe operation by preventing excessive heat build-up, but will also prevent the fan and motor from becoming a source of potential ignition by keeping temperatures below any auto ignition temperatures.
For those of you who are unfamiliar with the make-up of an industrial fan suitable for potentially hazardous environments, ATEX fans are constructed and classified in two parts, one label that explains the motor classification and protection, and secondly a rating for the overall fan construction including the casing, impeller, and materials. Part of the motor classification shows the end user the maximum surface temperature that the motor is limited to reach to prevent component getting so hot that it initiates the auto-ignition temperature of the surrounding flammable substances.
Your fan supplier should always ask for your hazardous area classification information, this will inform them of the gases or dusts present, their presence to determine the ATEX zone, the temperature limitations that must be considered, the materials required to ensure longevity and safe operation and the level of ATEX protection required from electrical components such as motors. Under DSEAR and ATEX legislation it is the sole responsibility of the end user to conduct or contract a hazardous area classification. Suppliers will not be able to supply equipment for hazardous areas without this information from the end users.