In this episode of the Dust Safety Science podcast, we interview Todd Siefke, Occupational Safety Officer at WorkSafe BC, about silo fire and explosion safety in wood pellet and agricultural product storage operations.
Todd shares his practical experience in the different types of silos and bin structures used in these industries. His insights have also been collected as part of a WorkSafe BC project dedicated to fire prevention, explosion safety, and structural safety in silos. While discussing this program and silo safety in general, Todd answers the following important questions:
- What should first responders be considering and what should the facilities that own the silos be considering when an incident occurs?
- What are some of the issues involving build-up of combustible gases and oxygen deficient conditions?
- What are the different issues that could arise during the fighting of these type of fires?
Silo Safety in British Columbia – a Project Overview
In recent years, there have been a number of fire and explosion incidents in BC involving silos used to store wood pellets. These incidents have raised the question of risk in not only this industry but other sectors that use silos to store raw material and finished product.
WorkSafe BC has launched an initiative to help silo owners and managers understand the risk of fire and explosion and take proper preventive or measures such as:
- Monitoring their silos
- Inspecting them regularly
- Keeping them in good serviceable condition.
If a fire or explosion does occur, the project also presents first responders with the best tactics for extinguishing it based on silo type and contents.
Silo Classification
The definition and use of a silo tend to vary from one industry to another. For example, in an agricultural setting, silos are the taller, oxygen-limited structures used to create silage for animal feed. Anything used for storing grain and other products is generally referred to as a grain bin: these structures tend to be lower in height and made from corrugated material. In the manufacturing industries, the term silo is used to describe the any vessel that stores bulk materials.
Silo Fires
Common causes of silo fires and the recommended emergency response depend on the silo type. Owners and managers need to consider the type of silo that they have, evaluate the risk of a fire in that structure, and understand what they need to do to extinguish it.
Causes
Silos that store biogenetic material such as sawdust, wooden pellets, grains, or silage could be susceptible to self-heating and spontaneous ignition, creating a smoldering fire. This has been identified as one of the most common causes of fires in the agricultural industry and has also been named as a suspected cause wood pellet fires.
It can take days to notice smoldering fires. In the interim, the incomplete combustion can cause gases to build up, one of them being carbon monoxide, which is also flammable and can cause an explosion in the silo.
Silo fires can also be caused by an external ignition source, such as:
- A hot bearing
- A spark traveling into a storage silo through a conveyance or ventilation system
- Static electricity from transferring of material
Risk Management
Any facility that stores material susceptible to self-heating, such as wood pellets and silage, can carry out routine temperature monitoring to detect heat build-up. In the case of silage, this monitoring can ensure that the heat doesn’t reach the point where the material will ignite.
Response
When it comes to extinguishing the fire, the recommended course of action depends on the silo type and its contents.
Oxygen-Limiting Silos
These silos are smooth, steel-walled structures designed to seal so that better silage can be produced. When used in other industries, they do a good job of keeping the product dry. The problem is that when a fire event occurs, any flammable gases such as carbon monoxide have no way of escaping and can build up in the headspace of that silo creating an explosion hazard. First responders may want to consider an alternate firefighting tactic such as using a nitrogen system.
Conventional Silos
Conventional silos are usually built using concrete staves held together by steel rods. Some are built from reinforced concrete, wood, brick, or glazed ceramic. These silos are filled and from the top. Their looser construction design and passive ventilation prevent the same build-up of carbon monoxide experienced by oxygen-limiting silos.
When determining a proper response to a fire incident, understanding the characteristics of the material being stored is important. For example:
- Some materials are so dense that a fire cannot exist within it. But if there is oxygen within the space, there may be air gaps that allow a smoldering fire to develop.
- Materials can be hydrophobic, meaning that they repel water, or hydrophilic, meaning that it attracts water.
Structural Safety in Silos
Silos are designed to hold a certain capacity and weight. If a fire occurs and emergency responders use water or a foam extinguishing agent, they must consider the weight of that water or foam in the silo. For example, wood pellets will absorb and retain water, which could potentially overload the silo and cause the structure to fail during a firefighting operation.
Similarly, if the silo is an oxygen-limiting type, there is a greater potential for dust or carbon monoxide to build up within the headspace and cause an explosion during firefighting operations.
Research into Silo Fires
For those wanting to research the causes of silo fires and different methods of extinguishing them, Todd recommends Silo Fires: Fire Extinguishing and Preventive and Preparatory Measures by Henry Persson. Contents include:
- Potential ignition sources
- Alternate firefighting tactics such as using an inert gas or using foam and water.
- Preventative measures that include preparation of nitrogen extinguishers based on silo size and the amount of gas needed.
Conclusion
There are different factors that come into play in silo fire and explosion prevention and response, particularly in silos containing wood pellets, agricultural products, and other materials. Educating facility managers on how to prevent incidents and first responders on how to effectively respond to them can minimize their impact, save property and lives, and hopefully limit the number of occurrences.
Resources Mentioned
The resources mentioned in this episode are listed below.
Fire and Explosion Incidents in BC
Explosion at Pellet Plant in Houston
Wood pellet fire in Prince George expected to burn for rest of week
Organizations
WorkSafe B.C.
Recommended Reading
Silo Fires: Fire Extinguishing and Preventive and Preparatory Measures
Previous Podcast Episodes:
DSS 007: Dust Hazard Analysis and Explosion Prevention with Dr. Ashok Dastidar
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DSS 008: Prevention and Response to Silo Fires with Todd Siefke of WorkSafe BC
