Canadian Biomass • Summer 2025 • Product diversification requires protections

When many sawmills and planer mills operated in the past, finding homes for their residuals outside of the mills was common practice. This may have meant sending green wood chips to a nearby pulp mill and sawdust to a medium-density fibreboard (MDF) manufacturer, or simply burning the residuals in beehive burners. But as sawmills and other wood products manufacturers across Canada identified the additional value in using 100 per cent of the log – both monetary and societal – they’ve also acknowledged the additional precautions needed to ensure operations remain safe.

“A lot of the sawmills are now using those residuals to add value to their process, whether it’s consolidating the material and using it as fuel in their biomass burners or creating wood pellets. I believe the mills are realizing the additional danger in the manipulation of those products,” says Neill Gibson, director of business development, sales and marketing for Rodrigue Métal Ltée. “When you think about a planer mill, obviously the lumber, the material, is dry, so they’ve got dry sawdust. They’ve got dry chips and wood shavings. In the past, those would be shipped off to other users and there wouldn’t necessarily be a whole lot of danger. Now with the integration of what they’re doing, all of a sudden they’re forced to look at the notion of dust extraction, the control of spark detection, sprinkler systems, etc.”

Dust mitigation and spark detection systems have come to the forefront for even the smallest of mill owners and operators.

“Instead of major industrial complexes producing pellets, or sawdust going to producers of MDF, now you’re getting mills taking these byproducts and doing something with it themselves on a smaller scale, and this means that they have to consider these productions differently than they would a traditional sawmill,” Gibson says.

Francis Petit, director of engineering for VETS’ Industrial, Mechanical & Ventilation Division, says the types of dust and explosion mitigation technologies have not trended to anything specific in recent years, but safety testing has been evolving.

“We see similar tech used; however, the safety testing for the technology has improved. Only vendors that work towards functional testing are being considered as NFPA compliant equipment, and we are replacing older pieces of equipment with similar, but tested ones,” Petit says.

When mills are deciding on the types of protection systems they require, they should first focus on the content of their materials.

“With sawmills, you generally have material that’s still wet, higher moisture content, so the risk of an explosion is much lower, but fire threat is still there. When you get to the point after material has been dried – whether it’s being used for biomass purposes or even for MDF plants – when that wood dust is dry, there is substantial explosion potential,” explains David Grandaw, vice-president of sales for IEP Technologies.

As a first step, Grandaw says companies should be looking at their facilities and identifying where the ignition points are, as well as the areas where they could have mechanical breakdown and some friction risks that could cause some smoldering or burning materials. This is where they should start to address detection and prevention measures.

“Then you consider an upset condition, do occasionally discover burning or smoldering materials, and how do you stop this material from turning into an explosion?” he says.

One of the common ways this can be done is through the use of a spark detection and suppression system.

“Spark detection and suppression systems are based on detection in the form of an infrared detector, or detectors, depending on the duct size, looking for a hot spot, typically a spark or burning ember traveling through a duct or on a conveyor, detecting it, and then, X amount of metres downstream based on conveying velocity, inject a water spray to suppress that burning ember before it gets into the downstream receiving vessel where it might find the right dust-air mix to start an explosion,” Grandaw explains.

There are a wide variety of technology suppliers in the dust and spark detection and suppression space, so selecting the right technologies for a plant requires the consideration of multiple factors.

“Like with any other technology, there are a number of considerations you have to look at when you put in one of these systems: What is the scale of the detection and protection required? What are your airflow velocities? Is the application out- side where you must heat trace the water pipes, since in the wintertime up in Canada, we don’t want pipes to freeze and break,” Grandaw says.

In sawmills in Canada and the U.S., dust collection systems are always located outside, so people tend not to consider them when they’re talking about the automation within a facility, Gibson notes.

“It’s almost secondary. So very often, there’ll be maximum two inspections annually where you’re going to be looking inside the system to see if there’s any escaping material, to see if there’s any gap in pressure, or anything like that. But the systems are standalone, and they operate on their own,” he says.

In the majority of European mills, the dust collection systems have been integrated into the main control centre of the mills and are treated more like part of the production line than as a secondary system, Gibson notes.

“That’s something that we need to look at on our end, moving towards an integrated system, having that data be collected within the same systems, and to be able to include that within all of the maintenance packages that exist for sawmills as a whole,” he says.

While cleaning up the air in closed-off production facilities is vital for the health of employees, mill owners also want to be able to recirculate the air back into their facilities as much as possible to reduce energy costs.

“Here in the north with colder climates in the winter, it’s one thing to clean the air, but that heated air, you don’t want to just exhaust it outside. You want it to be clean enough to reintroduce it back into those buildings. That brings in a whole other series of rules and regulations, because it’s people’s health. So, it’s interesting to see how the systems are evolving,” Gibson says.

His company has been offering these systems for over 60 years to their customers in Quebec due to the colder climates, and it’s something that is increasing in demand for mills in the north and south.

“Sometimes it’s not even keeping the heat in, it’s keeping the cool to recirculate the air,” Gibson says, referring to mills in the southern U.S. “Planer mills, especially the high-production planer mills, they’re all closed systems. You’ve got dust collection in there. You want to keep any cool air in that you can. Therefore, you’re cleaning the air, removing the particles, so that you can reintegrate that cooler air.”

The systems for cleaning and recirculating heated air or cooled air back into a building are largely the same. The key factor to consider for both is moisture management.

“Condensation within the piping is one of those things that you’re having to deal with. So, you’re insulating the pipes here in the north to keep the heat in and to avoid condensation, and the same thing in the south, but it’s cold air on the inside versus the outside,” Gibson says. “The systems exist in terms of open systems, where they’re venting directly outside. It’s less expensive because it’s less piping. But when you’re looking at energy costs, when you’re looking at what’s going out into the environment, sometimes having that closed system and bringing the air back into the building is the best way to go. We’re seeing more and more customers going for the idea of closed systems to keep that heat or cool inside the building.”

When it comes to explosion venting options, there are standard and flameless options. A flameless explosion vent consists of a vent panel surrounded by a metal mesh or other means to act as a heat sink to absorb the heat from the flames, so all that is released to the outside during an explosion event are hot gasses with no flames.

“That’s a very common technique that can be used in areas where standard explosion vents aren’t suitable,” Grandaw explains.

Standard explosion venting is a much less expensive option than flameless vents, so has historically been the preferable protection measure for a customer in the wood products industry. However, flameless venting is a good option for plants that cannot redirect potential fireballs to a safe area.

“In those cases, the flameless venting makes a good alternative,” Grandaw says. “I did a calculation on a vessel once that indicated 114 feet was needed for flame ejection distance. That was unusual, as that was for a very large vessel. But 30 or 40 or 50 feet is not unusual.”

The NFPA 68 Standard offers a formula for measuring safe flame ejection distance. Additional thermal effects must also be considered, as the heat generated from an explosion can travel farther than the fire and can still be hot enough for someone to be injured or worse.

One of the biggest challenges for some wood products manufacturers keeping current with the latest dust and explosion mitigation technologies has been a misinterpretation of the standards that results in plants using the wrong technology for the goals of the safety standard, Petit notes.

“We have seen plenty of spark detection systems as the only line of defense, in place of explosion isolation,” he says. “Catching up with the current standards is not incredibly hard; as in, we are not seeing any drastic changes of the methods of mitigation being changed drastically with each revision.”

Some companies want to continue using legacy systems instead of purchasing new systems, but this can be an issue as older standards may have been originally misinterpreted and were always deficient, Petit adds.

Luc Cormier, explosion protection consultant for Fike, says Canadian facilities are probably less protected than the U.S. facilities overall due to there being less requirements in Canadian standards relating to combustible dusts compared to the U.S.

“Most sawmills would need traditional explosion protection (e.g., venting or suppression) on some vessels handling their dry materials, spark detection and extinguishing systems where saws, mills or sanding equipment are tied to dust collection systems, and deflagration isolation on any vessel having an explosion hazard. This along with housekeeping procedures to limit dust accumulation inside the facility would go a long way. However, in most cases, I see one or two of these safeguards provided, with some equipment having no protection at all where there should be protection,” Cormier says.

Another major challenge can be the age of the mills, and the cost involved in retrofitting the equipment.

“A lot of these facilities tend to have older equipment which might be difficult to retrofit, and cost of upgrading to a fully compliant facility may be prohibitive for a lot of these sawmills, which is probably one of the biggest obstacles they face,” Cormier says.

Grandaw says price is a major factor for wood products plants when looking at whether to install passive or active dust and explosion mitigation and suppression systems. “Not only initial cost, but long-term cost of ownership, because passive systems do not typically require the maintenance that an active system would. Active systems need to be inspected, just like any other process area of the plant. Usually, since these are specialized systems, you would have the manufacturer send their own field technicians to do that inspection. So, the cost is much higher to maintain the active systems than the most passive systems. Passive systems are things such as the flap valves, standard and flameless vents. Those require mostly visual inspections so they can be done at the plant level. So, the long-term cost of ownership is less.”

Petit offers sawmills and pellet plants the following tips for optimizing their dust and explosion mitigation operations:

• Keep the records/drawings of the duct layouts and capture the changes made. This way a technical review is possible without wasting too much time and resources.

• Expanding a system is more technically challenging than it seems. Consult with the original designer.

• Containment of the dust-generating equipment will reduce wasted air from the exhaust system.

• Keep the Dust Hazard Assessment (DHA) up to date. It should be reviewed every five years or every time the process or dust changes

• Training of staff around the hazard and how to maintain safety equipment is also a key factor in mitigating the hazard.