The burning of wood and other fuels in wood stoves, ovens or fireplaces results in the gradual buildup of soot, creosote, resin and other combustible materials on the interior surfaces of chimney stacks. Burning of so-called "green wood", which is freshly cut wood that has not been allowed to cure or age adequately, especially contributes to residue buildup.
Fires in chimney stacks are common occurrences especially in rural and recreational areas where use of wood burning stoves is prevalent. Proper cleaning of the chimney stack on a regular basis reduces the risk of chimney fires. The choice of fuel to burn also reduces fire risk, since burning of soft wood, paper, plastics and garbage greatly increase the buildup of combustible material.
However, in many cases the risk of chimney fires is a significant matter especially in rural areas where fire fighting response is relatively slow and lacking in equipment. In many cases, wood burning stoves use sheet metal cylindrical chimney stacks. The sheet metal stack offers very little resistance to fire spread and the chimney fire rapidly spreads to the interior of the building.
Conventional fire fighting methods include climbing on the building roof and spraying water down the chimney stack. This method is of course only practical if the fire has not spread significantly to the roof of the building by the time fire fighters arrive. It also results in significant water damage to the building interior.
Use of a hand held portable fire extinguisher is possible however such a method is risky and often ineffective. A chimney fire generally occurs within the enclosed stack above the damper which obstructs access and flow of extinguisher compound. In addition, to access the burning interior of the stack, first the fire in the wood stove itself must be extinguished. The user must then insert the portable extinguisher inside the hot smoke filled stove and properly aim the fire extinguisher nozzle up the stack without burning himself. Due to the obstruction of the damper and frequent bends in the stove flue or chimney stack, the rapid delivery of fire extinguishing compound to the area of the stack under fire is doubtful, risky and inefficient.
Conventional responses to this problem have been partially successful, however, complex or costly fire extinguishing systems are very unlikely to be widely adopted for very simple reasons. Wood burning stoves are used because the fuel is relatively inexpensive. Purchase of an elaborate expensive fire extinguishing system is unlikely. Wood burning stoves are also usually installed by homeowners or other relatively unskilled persons for their own use. Complicated fire extinguishing systems are unlikely to be properly installed or even purchased by such users.
Examples of relatively complicated fire extinguishing systems are described in the following United States Patents: U.S. Pat. No. 4,194,570 to Arenciia, Jr.; U.S. Pat. No. 4,872,513 to Gardner et al; and U.S. Pat. No. 4,434,784 to Van Patten.
In U.S. Pat. No. 4,481,933 to Sawtelle, a simple access tube is mounted to a horizontal sheet metal chimney stack. The tube has a bent right angle to aim fire extinguishing compound downstream from the damper. A portable fire extinguisher is positioned at the outer end of the tube to spray fire extinguishing compound inside the chimney stack.
The primary disadvantage of Sawtelle's system is apparent when the device is installed in a vertical chimney stack. Most chimney stacks are in fact primarily vertical. The use of a vertical stack efficiently exhausts hot fumes and minimizes resin buildup inside the stack.
Use of Sawtelle's system on a vertical stack would result in backflow of cinders, ashes and other solid particles. The solid particles can fall down a chimney stack into the inner open end of the tube and out into the occupied building. Backflow of solid particles through the tube can cause fires within the building as cinders fall on combustible materials such as carpets, papers and wood floors. Since the open inner end of the tube must face upward to direct spray up a vertical stack, use of Sawtelle's device in a vertical stack would subject a building and occupants to an unacceptable risk of fire. At the very least, the backflow of solid particles results in a sprinkling of adjacent areas with black soot, and at worst presents a serious risk of injury to people and property.
It is desirable therefore to produce a safe, simple and inexpensive device to provide access to the interior of a chimney stack in the event of chimney fire, while minimizing the risk of backflow. Preferably the device is simple enough to enable use of commonly available tools and require a low level of skill.