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February-March, 2001 |
Rotary Saws and Chain Saws
When opening the compartment doors of a typical fire engine in the United States, a wide variety of tools and equipment will normally be observed. The variety of tools and equipment is generally based on a combination of tradition, NFPA standards, district needs, and the always popular “its always been there.” Standard tools and equipment that readily come to mind are the pike pole, pick-head axe, ground ladder, and rotary saw. However, a tool that is becoming more popular, due to its effectiveness, is the chain saw. While the rotary saw and chain saw have similarities, they can also be diametrically different in their application. Let’s take a brief look at their advantages and disadvantages and review several operational considerations.
ROTARY SAW
The venerable rotary saw is an excellent multipurpose tool that is versatile and effective in a variety of applications, depending on the blade used. Cutting thick or heavy roof composition normally found on older roofs, metal deck roofs, lightweight concrete roofs, and metal in forcible-entry applications readily come to mind. However, several noteworthy disadvantages should also be considered when using this power saw. These disadvantages are as follows:
The blade can continue to spin after the throttle is released or the saw is shut-off.
A rotary saw can exhibit a gyroscopic effect that is caused by the spinning blade. Depending on the cutting angle, this can cause the saw to be unwieldy.
Depending on the size of the saw and blade, the depth of cut is normally limited to 3.5 to 5 inches deep, with 4 inches being the norm.
In some applications, a rotary saw can be heavy and difficult to operate in precarious conditions. As an example, while operating from a roof ladder, try to reach out with this saw to cut a ventilation opening.
To obtain the maximum benefit from a rotary saw, evaluate the following considerations:
First, always wear the appropriate safety equipment when operating the saw.
Second, due to the versatile nature of the saw — its ability to use a masonry, wood, or metal cutting blade, determine the primary use for the saw and equip it appropriately as follows:
If the primary use is ventilation in wood roofs, mount a carbide tipped wood cutting blade.
If the primary use is forcible entry, mount a metal cutting blade.
Third, most rotary saws will allow the blade to be mounted in the inboard or outboard position and positioning is easily accomplished by rotating or reversing the bar that holds the blade (be sure to check the operator’s manual for your saw). As an example, if a rotary saw is used for ventilation operations, mount the blade in the inboard position, as this will minimize the gyroscopic effect by centering the blade with the saw. However, if the saw will be used for forcible entry operations, mount the blade in the outboard position. Although this will maximize the gyroscopic effect, it will allow the blade to be inserted into areas with minimal space constraints (i.e., sliding the blade under a tempered glass door to cut a pivoting bolt on the lock at the bottom of the door).
Fourth, while cutting a surface, most firefighters will hold the saw off of the surface. This can place unnecessary weight on the back muscles and enhance “binding” the blade in the cut. To minimize this problem, place the saw on the surface to be cut and pull the saw into the cut. This will allow the saw to glide on the blade guard and lower portion of the carrying handle, allowing the surface to support the weight of the saw and center the blade in the cut.
Fifth, when cutting a surface with a rotary saw, the operator must back-up or walk backwards. Therefore, use a safety person to watch the overall operation and the area behind the person using the saw.
CHAIN SAW
The chain saw can also simplify numerous operations. However, compared to the rotary saw, the chain saw is not as versatile and is limited to primarily cutting operations in wood. Yet, the recent focus (and need) for aggressive ventilation operations on the modern fireground has placed a great deal of emphasis on timely and safe horizontal and vertical ventilation operations, especially vertical ventilation. When considering vertical ventilation operations on roofs (which are normally wood), the power-to-weight ratio, reach, and lighter weight of a chain saw can be a significant advantage from the perspective of operational efficiency and safety, as compared to the rotary saw. However, several noteworthy disadvantages should be considered when using this power saw. These disadvantages are as follows:
Chain saws were not originally designed for fire department operations. An ill-equipped saw in concert with an engine displacement that is not sufficient for the specific needs of a district will not be a favorite tool of fireground personnel.
Depending on the length of the bar, there can be a considerable amount of exposed cutting teeth. Therefore, it is imperative that personnel moving a running chain saw move with safety (operator and other personnel) as a prime consideration.
If a chain saw is not operated correctly, it can “kick back.”
A chain saw can be a powerful and safe tool if operated within appropriate safety guidelines. However, if personnel have not received adequate training, the saw should be left on the apparatus. To obtain the maximum benefit from a chain saw, evaluate the following considerations:
First, always wear the appropriate safety equipment when operating the saw.
Second, as necessary, practice with the saw to develop a “feel” for the saw and its capabilities (which can be impressive).
Third, when cutting with a chain saw, the operator must back up or walk backwards. Therefore, use a safety person to watch the overall operation and the area behind the person using the saw.
Fourth, some chain saws can be purchased or retro-fitted with a protective cover (i.e., guard/depth gauge) over the bar and chain. This device will protect personnel from the cutting teeth and can be adjusted to allow the saw operator to monitor the depth of cut.
A chain saw properly equipped for fire department operations should be equipped with the following items:
Minimum 68cc to 72cc or 4 cubic-inch engine. This will provide adequate power for wood roofs with light and heavy coverings. Remember that municipalities located at above average elevations (i.e., 5,000 to 7,000 feet), with heavy roof coverings, may require a larger engine. As an example, a chain saw operated at 7,000 feet will have a 30 percent power loss. NOTE: Newer saws are more tolerant to elevation changes due to EPA regulations requiring cleaner burning engines. Additionally, it will not be possible to adjust these carburetors for maximum performance.
An 18-to-20-inch bar. This will allow good “reach” with the saw (important when working from roof ladders) and allow the saw operator to stand fairly erect while cutting. This minimizes weight on the back muscles and maximizes the distance between the surface being cut and face of the saw operator.
Sprocket tip bar. A “hard nose bar” can cause unnecessary friction that will result in a slower chain speed and elevated chain temperatures. This causes the chain to stretch and droop after cutting. A bar with a sprocket on the end of the bar that turns on a roller bearing will result in a faster chain speed and reduction of chain temperatures by as much as 170-degrees. This minimizes chain stretch and minimizes the chain melting the tar in roof coverings during cutting operations. To further reduce the weight of a chain saw and increase the hardness of a bar (longevity), titanium bars can be purchased. NOTE: Regardless of the type of bar used, standard motor oils (i.e., 30 weight, etc) or oil mixed with various types of thinners should not be used. This will minimize lubrication at the tip of the bar and dramatically accelerate wear. Always use bar oil designed for your chain saw.
Muffler guard. A simple piece of aluminum or thin steel mounted to the front of the muffler will dramatically reduce maintenance by keeping the saw cleaner during cutting operations and debris from adhering to a hot muffler. NOTE: The food-release product PAM can be applied to a clean bar, muffler guard, and engine to further reduce maintenance. This will minimize oils and debris sticking to the treated surface.
Large air cleaner. A larger than normal (normal as in a standard chain saw) air cleaner will provide an increased filtering area in smoky conditions.
Carbide-tipped chain. All carbide chains are not created equal, and carbide chains are vastly superior to standard chains for roof ventilation operations. It is strongly recommended that you “try before you buy.” A new type of carbide chain referred to as the “Bullet Chain” has proven to have excellent cutting speed and longevity and will easily cut 18-gauge metal with minimal detrimental effects to the cutters. For maximum effectiveness, this chain requires a saw of at least 4 cubic inches, and chain pitch of .404-inch to .063 gauge. A chain saw with a torque curve near the maximum RPM of the engine is also recommended for best results.
Accessible tool for adjusting or replacing the chain. Buy a short piece of 1/4-inch or 3/8-inch fuel line and tape it to the side of the saw’s hand guard. Insert the chain tension-replacement tool into the fuel line. The tool will now be with the saw when you need it, not on the apparatus in the street.
Carrying strap. This type of strap will allow personnel to carry a chain saw, leaving both hands free to climb ladders, etc.
Last but not least, consider today’s gasoline. Modern gasoline is significantly different from the gasoline of yesterday, and has numerous additives (i.e., alcohol, MTB, oxygenating agents, etc.) that can be detrimental to two-stroke engines (chain or rotary saws). Therefore, ensure your gasoline is fresh (definition: change at least every 30 days) in your supply cans and in your power equipment. A good gas additive such as an octane booster will also keep your gasoline fresher longer but will not solve the additive problem. One solution to the additive problem (depending on your area and the additives used) is to run a 50/50 mixture of pump gasoline and racing gasoline.
EDITOR'S NOTE: Portions of this article appeared in National Fire and Rescue Magazine and Chief Mittendorf’s book Truck Company Operations, published by Pennwell. Truck Company Operations can be purchased by clicking here.
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