By Ben Peetz
Drying equipment comprises an important part of many industrial and manufacturing operations. Although drying is often located outside of a facility, because this process often comes in the midst of a manufacturing cycle, the equipment can also be found deep within a large facility. When one of these systems catches fire, firefighters may face several challenges in finding and accessing the area of involvement.
Drying processes are used in industries ranging from steel fabrication to wood products to grain crop production. The energy applied in such a process can range from forced-air heat to infrared energy to UV light. The drying operation may be designed to alter the raw material, or it may be applied to cure or otherwise activate a modification being made through the particular stage of manufacturing.
In some facilities, dryers may be used simply to cure a coating. However, the actual coating product and the specific substrate material often greatly determine the type of dryer that can be used and the hazard that the process presents. Processes involving steel fabrication often use forced-air heat or infrared energy to heat the entire item to temperature, thus curing the coating and affixing it permanently to the end product.
This process may also be used in industries where the material is combustible, such as lumber and other wood products. Sawmills regularly use drying kilns to elevate the temperature of newly sawn lumber, thus driving out moisture and enhancing the qualities of the wood for use in any variety of applications. Some drying kilns may be heated by a direct-fired forced-air stream; others are heated indirectly by steam provided by a boiler system. Because the lumber in a drying kiln is stacked with aeration sticks to allow air flow between the boards, there is an enhanced risk for a fast-burning fire to occur. In these cases, firefighters must be familiar with the type of kiln and take action that does not necessitate the opening of the doors. The introduction of additional air through the opening of doors almost guarantees a catastrophic loss of both the lumber and the kiln. If there is a fire in these structures, the doors should be kept secured, and aeration fans should be turned off. Some kilns allow for the introduction of raw water or steam for the conditioning of lumber, and this may also work as a fire suppression tactic.
In other wood industries, like assembled furniture, the product cannot be raised to cure temperature without potentially affecting the quality of the product because of characteristics like glue joints and substrate integrity. In these cases, a forced air oven may blow heat across an object for a period of time without raising the internal temperature completely. Other technology is also now being used in these cases; they include near-infrared drying lamps that heat the surface of an item to a cure temperature and cycle on and off to prevent the internal temperature from rising.
Yet other more advanced systems use UV curing stations. The UV light cures the surface of the product, with very little change in surface temperature. These systems, however, pose other dangers to firefighters, as the equipment is heavily electrically based. Also, the coatings can be very hazardous when coming in contact with skin, as they are designed to absorb UV light and can effectively give a patient a severe sunburn.
As with lumber, dryers in other wood processes and in agriculture industries are used to remove moisture from commodities to promote a more efficient use of the product, prolong storage life, and limit decay. A specific moisture content may be needed for the grain to be used, affecting characteristics like feed value and the ability to grind or flake. Farms and grain elevators often have dryers on site that will process the grain as it is harvested.
A tower dryer is a structure used for drying “wet” grain as it comes from the field down to a moisture content suitable for long-term storage of the grain. For example, corn may be harvested at 20 percent to 25 percent moisture, but for long-term storage, this number must be reduced to 15 percent or less. To do this, farmers and grain handlers may use gas-fired drying equipment, which may be a mobile unit, a part of a structure, or an independent free-standing structure. Some dryers take the grain from a wet-storage holding bin and pass the grain through the drying equipment before it exits into a long-term storage structure. Other smaller, simpler systems perform the drying within the long-term storage structure.
The key approach to handling a dryer system fire is to understand how the system is designed. This is important so you know how to shut down heat systems and blower fans, as well as stop the flow of product, thus isolating the burning material from undamaged product and structures. It will also help you determine the amount of product involved and how to access the fire. Many systems are designed with automatic conveyance systems that will move product through a system from start to finish unless an operator stops the flow. Operators should be trained to stop the process in an emergency, but this may not always happen, and firefighters will need to quickly assess the situation to determine how to best limit the spread of a fire.
In the case of a pass-through dryer system where the product itself moves within the equipment, it may be possible to purge the product from the unit. However, if a system is still operating during a fire, the burning product may be conveyed into a storage structure, creating additional fire involvement and posing some serious challenges for extinguishing a fire.
Always keep in mind the potential for a dust explosion wherever dusty product is burning within a compartment, as well as the potential for a backdraft situation when fires occur within oxygen-limiting structures.
Most mobile and stand-alone drying equipment have perforated components, which will provide for the infiltration of water when applied to the exterior.
For all structures, be aware of the potential for collapse if it is heated to the point where the components weaken. Do not place personnel in harm’s way, and keep this in mind when positioning apparatus.
BEN PEETZ, CSP, CFPS, is a second-generation veteran with the Napoleon (IN) Volunteer Fire Department, where he is assistant chief and has worked for the past 25 years. Previously, he had served in various capacities. He works full-time as a risk control consultant in commercial insurance and specializes in large farms and commercial agribusiness.