Industrial environments can be dangerous places due to the types of materials handled and potentially risky work practices such as safety shortcuts. This is especially true for facilities handling flammable liquid and/or those with significant amounts of combustible materials such as metal or organic dust. These types of operations are commonplace throughout the country, with many becoming desensitized to the risks they carry for personnel and those in the surrounding area.
Generally speaking, when discussing combustible materials the primary types will be either a flammable liquid with a low flashpoint or a type of dust made of metal or organic material such as wood, pulp or trash that can be ignited and result in an explosion. These materials are found in all sorts of different industrial processes, such as paper mills, grain elevators, foundries and machining plants. Because of the ubiquitous nature of this type of hazard, it is critical for workers to understand the specifics surrounding the different classes of fire and the specific materials associated with them. Combined with active safety measures such as barriers, warning lights
and the issuance of PPE for personnel.
Classes of Fire
Below are a listing of each of the five classes of fire relevant to industrial applications with combustible dust or liquid.
This type of fire consists of ordinary combustibles such as wood, paper, trash or anything else that leaves an ash. Water works best to extinguish a Class A fire.
These fires are fueled by flammable or combustible liquids, which include oil, gasoline, and other similar materials. Smothering effects which deplete the oxygen supply work best to extinguish Class B fires.
Energized Electrical Fires are known as Class C fires. Always de-energize the circuit then use a non-conductive extinguishing agent. Such as Carbon dioxide.
Specifically referring to combustible metal fires. Magnesium and Titanium are the most common types of metal fires. Once a metal ignites do not use water in an attempt to extinguish it. Only use a Dry Powder extinguishing agent. Dry powder agents work by smothering and heat absorption.
Encompassing fires that involve cooking oils, grease or animal fat and can be extinguished using Purple K, the typical agent found in kitchen or galley extinguishers.
For industrial processes, there are five primary classifications of fire – Class A, B, C, D and K. These are divided up based on the type of fuel they burn, which will affect the way in which they are managed. It should be noted that these fires will either be created by a combustible liquid or dust, which are usually involved in primary or secondary explosions respectively.
Primary explosions or fires are usually caused by liquids of some type, usually those that vaporize to form a ignitable mixture in the air. The temperature at which a liquid can vaporize is known as its flashpoint, which is a key factor in its danger. Essentially, the lower a liquid’s flashpoint, the more likely it is to ignite under normal circumstances, making it inherently more hazardous around potential sources of ignition such as exposed electronics, electrical connections, flame, etc. It should be noted that primary fires can also be caused by solids or dust but this is relatively uncommon as it is considerably more difficult to accidentally ignite these types of materials without an existing fire.
Secondary explosions or fires are by definition caused by primary fires, and typically involve materials that would not normally combust on their own without a massive ignition source. Usually secondary explosions are fueled by combustible dust
which is usually metallic or organic in nature. Certain types of metallic dusts are exceptionally combustible, such as magnesium or titanium. Commonly seen in industrial environments, the fires resulting from metallic dusts can be particularly dangerous.
While many people can readily understand the dangers associated with metallic dust fueling secondary explosions, organic dust often flies under the radar but is just as dangerous. This type of dust is more ubiquitous than metallic dust, seen in everything from farm operations to large scale industrial operations such as paper mills, chemical plants, pharmaceutical manufacturing plants, trash faculties and recycling centers. With these types of dust, the sheer quantity normally present in these facilities can mean the secondary explosions can be quite large.
Sound like a lot?
An easy way to remember these types of Fires is Class A leaves an Ash, Class B boils, Class C has current, and Class D has Dense Material and Class K for Kitchen.