Back to Basics: November 2013
By Mark van der Feyst
One of the functions of a truck company is to ventilate and force openings within a structure.
By Mark van der Feyst
One of the functions of a truck company is to ventilate and force openings within a structure. Some fire departments have rotary saws on their apparatuses to complement the equipment needed to ventilate buildings and to force different types of openings. This valuable tool, which has many benefits, such as portability and power, should be used more often.
The rotary saw can be carried anywhere on the fire ground, including to the roof of a building and up and down ladders. The rotary saw weighs between nine and 16 kilograms (20 and 35 pounds) without fuel. One firefighter can carry the saw either with the handles or using a strap attached to the saw. The strap can be made from webbing or even a used seatbelt. Having a strap frees the firefighter’s hands so that he or she can carry other tools or have both hands available for climbing a ladder. The rotary saw is portable enough that it can be used in small spaces, such as a trench for auto extrication purposes, provided there are no explosive gases present.
All rotary saws are powered by internal combustion engines – two-stroke, small gas engines. The small engines can range from 74 cubic centimetres (cc) to 119 cc in displacement with horsepower ranging from five horsepower (hp) to 8 hp. Due to this high output of power, the saw produces blade speeds from 4,700 revolutions per minute (r.p.m.) to 5,400 r.p.m. This allows the saw to cut through almost any type of material for which the blade is designed and rated. The blade size also varies from 30.5 to 40.5 centimetres (12 to 16 inches).
|Photo 1: Diamonds are embedded into the edge of the multi-purpose blade to create an abrasive cutting surface.|
|Photo 2: This Warthog blade features long teeth that protrude from the blade’s centre, making it great for cutting wooden roofs and siding products.|
|Photo 3: The Bullet Blade is a hybrid version of a vent saw chain and a rotary blade. It has, so far, proven itself to be a true multi-purpose blade.|
|Photo 4: A diamond-tipped blade will produce sparks when cutting metal objects, which can be hazardous for first responders.|
There are many types of blades on the market; when purchasing a blade, a department should consider its own needs. A multi-purpose blade with a diamond cutting edge is most common. It can cut through a wide range of materials with just one blade (see photo 1). Small diamonds are embedded into the edge of the blade to create an abrasive cutting surface. Over time and with consistent use, the edge of the blade can gum up with material that is being cut. This prevents the blade from cutting effectively. When this happens, momentarily bury the blade into new or clean material while it is running for about 20 seconds so that the cutting edge is cleaned. The blade can then be re-applied to the previous cutting operation; you will see a noticeable change in the cutting effectiveness.
Over time, the small diamonds of the blade disappear due to wear from cutting operations. Those small diamonds that fall off or disappear are replaced with newer diamonds that are embedded below the surface of the previous layer.
In photo 2, you can see another version of a rotary blade. This blade is known as a Warthog blade. You will notice the long teeth that protrude from the blade’s centre – this blade resembles the blade used for a table saw or a skill saw. This type of blade is great for cutting wood roofs and some siding products. At high speeds or revolutions, this blade can be dangerous for those near the cutting operation: the blade will quickly rip through bunker gear and flesh. Also, these blades are not designed for a specific brand of rotary saw, so be sure to check with the manufacturer to see if this blade is compatible with your department’s rotary saw.
A new blade that will be on the market soon, pictured in photo 3, is called the Bullet Blade (to learn more about the Bullet Blade, see the TechSmart supplement in the September issue of Fire Fighting in Canada). It is a hybrid version of a chain used for a vent saw and a rotary blade. It has, so far, proven itself to be a true multi-purpose blade. The chain that is wrapped around the outside of the round blade is the same chain used along the bar of a vent saw. Having the chain wrapped around a rotary blade enables it to spin three times faster. This increase in speed allows the chain to more effectively cut through more types of materials. In several video demonstrations of the new blade on YouTube, it is used to cut through vehicles, concrete, 2.5-centimetre (one-inch) metal pipes, shingled roofs, metal roofs, sheet metal ventilation hoods, cement blocks, glass windshields, and a host of other materials. The video shows the effectiveness and versatility of this blade under duress – the blade even maintains cutting precision with teeth missing.
Another advantage of the Bullet Blade is that it can be sharpened, the teeth can be replaced and the blade can be used over and over again. As opposed to a regular diamond-tipped blade, which will last only as long as the diamonds are present, the Bullet Blade extends the blade’s life; it also produces minimal sparks when cutting through metal objects. As shown in photo 4, when using a diamond-tipped blade, a rooster tail of sparks is generated quite easily; this is hazardous to the person using the saw and any others standing nearby. The sparks are a source of ignition if there are gases present or flammable objects nearby.
The rotary saw is a valuable piece of equipment on the fire ground and should be used more often. If your department is considering buying a rotary saw, know that it will be a more effective tool than a vent saw, especially when the Bullet Blade comes on the market.
Next month, we will look at operating the rotary saw, particularly with respect to different positions in which to hold the saw while cutting, as well as some safety points to keep in mind.
Mark van der Feyst is a 14-year veteran of the fire service. He works for the City of Woodstock Fire Department in Ontario. Mark instructs in Canada, the United States and India and is a local-level suppression instructor for the Pennsylvania State Fire Academy and an instructor for the Justice Institute of British Columbia. E-mail Mark at Mark@FireStarTraining.com