The radial arm saw: danger in the workshop.
Nevertheless, it shares with other power saws the ability to do tremendous damage to a hand or other body part that comes into contact with the blade or another rotating part of the tool. Also, its particular characteristics create other serious and unique dangers.
The radial arm saw consists of a motor drive and carriage that move along a mounting arm suspended over the cutting table. A circular saw blade, typically 10 inches in diameter, is secured to the shaft of the motor drive. In cross-cut operations the user pulls the carriage toward him or her, and the saw blade - extending from above the work to slightly below bench level - saws through the wood.
The mounting arm can be adjusted and locked at various angles. This allows the user to make accurate 90-degree cuts as well as cuts at other angles. For ripping operations (sawing the wood parallel to the grain), the user turns the carriage so that the side of the blade is parallel to the rear fence of the tool. Long boards can then be fed from the side.
The radial arm saw is quick and efficient, but safety hazards unique to its design sign can cause serious injuries.
Some models pose a serious risk of the carriage flying back and striking the user - with the blade still turning - during cross-cut operations. This can occur if the rotating blade happens to touch the edge of the wood on the table.
The carriage of the radial arm saw moves freely along the mounting arm. Because the wood is held stationary in the rear by a fence, the wood cannot be flung back toward the operator. (This "kickback" occurs commonly with conventional bench saws, which require the board to be fed into a rotating blade projecting up through a slot in the table.)
Because the wood is held firmly in place, if the rotating blade inadvertently bumps the edge of the wood, the carriage call be propelled violently toward an operator who has completed a cut and released the handle of the tool. The energy contained in the rotating blade is unable to shift the wood rearward, so it impels the carriage-and-blade assembly forward toward the operator with great speed and force. (The action is similar to what happens when a car wheel begins to turn: Since the road is stationary, the car begins to move.) If the hand of the operator is in the path of the blade, serious injuries can occur.
Even if the saw is equipped with a lower blade guard, it may not be able to prevent the injury. If the guard is designed to ride up over the wood being cut, it can ride up and over a human hand just as well.
Saw manufacturers typically deal with this danger by cautioning the operator in the owners manual to keep hands out of the path of the blade. This warning is hardly effective if the operator is not aware of the ability of the rotating saw blade to fly back.
Several safety features could be built into the radial arm saw to control the flyback problem. A few examples follow.
Safety lever. There is never all operational reason for the carriage to move toward the operator when the operator's hand is not oil the handle. Flyback injuries could be avoided if the handle were equipped with a lever that would prevent the carriage from moving toward the operator except when the lever was depressed. This feature could be easily adapted to the saw's design and would not interfere with normal sawing.
Sears, Roebuck and Co. has adapted the safety lever concept in an interesting and novel way.(1) This lever does not affect the movement of the carriage; rather, it controls a guard over the lower part of the saw blade. When the user activates the lever, it raises the guard. When the user releases the handle, the guard over the front of the blade.
Although this system does not control carriage movement, it tends to prevent flyback by preventing accidental contact by the blade with the wood on the table. Even if a flyback occurs, the guard, covering the blade, will prevent injuries to the operator.
Speed control. Because there is never a need for the carriage to move rapidly, either toward or away from the operator, a speed control feature could be provided to keep the rate of movement to safe low levels. This concept was applied in the design of auto seat belts, which permit slow adjustment for comfort but which lock up and constrain the occupant when a preestablished speed is exceeded.
Several speed control devices have already been patented.(2) least one Japanese saw manufacturer provides this feature as both original equipment and as a retrofit kit.(3)
Trigger switch. The flyback danger is exacerbated because the radial arm saw, unlike the hand-held power saw, has no trigger switch; it continues to run at full power until the power switch is turned off. This feature is necessary during ripping operations when the operator must use both hands to control the wood being cut. During cross-cutting, however, there is never a need for the saw to run when the operator's hand is not on the control handle.
Manufacturers could easily provide a three-position power switch with an "off" position, a "full on" position for ripping, and a "trigger on" position for cross-cutting. This feature could be made automatic by wiring the trigger to be constantly on only when the carriage is in the rip position. When in the crosscut mode, the unit would require constant pressure on the trigger.
Automatic brake. An automatic brake can bring the blade to a stop in 3 seconds or less after the trigger is released. A saw without this feature takes 10 or more seconds to coast to a stop. Black & Decker included an automatic brake on a hand-held circular saw series as early as 1965. It is present on many current models of radial arm saw.(4)
The saw is clearly safer when the blade is braking to a stop than when it is rotating under full power. Moreover, there is little evidence to support the claim that the automatic brake causes undue wear on the motor.(5)
Auxiliary Shaft Problem
Certain radial arm saws are equipped with an auxiliary shaft on which the user call mount an attachment, called a chuck, for a drill or router bit. This allows the user to convert the saw into a drill press of sorts by removing the saw blade, mounting the drill bit on the chuck, an rotating the carriage 90 degrees to move the drill bit into a vertical position.
The danger here lies in the possibility that the operator will forget to remove the drill bit when converting the unit back to the saw configuration. The bit is then in a horizontal position. If the carriage is propelled forward in a flyback, the rapidly rotating drill bit might strike the operator and inflict serious injury.
One simple way for manufacturers to avoid this hazard is to equip the saw with only one mounting position for the saw blade or drill chuck. The operator would then have to remove the chuck to mount the blade. It would be impossible to have both tools in place at the same time.
Contrary to common belief, no mandatory standards regulate the manufacture of radial arm saws - or, indeed any other power saws.
A nonbinding advisory standard issued by the American National Standards Institute and Underwriters Laboratories, Inc., falls short of providing adequate protection.(6) For example, the standard requires the saw to stop within 15 seconds after it is turned off. The technology for stopping within 3 seconds has been available for decades. A mandatory standard of the Consumer Product Safety Commission requires that a lawn mower stops within 3 seconds of the time the operator releases the handle.(7)
The 15-second "requirement" clearly provides minimal protection to the user. One need only imagine what a rotating blade can do to human flesh and bone in 12 seconds.
The assessment of a case involving injuries caused by a radial arm saw should begin, as it does in all products cases, with a comprehensive understanding of how the injury occurred. The attorney must also understand the relationship between the event and the tool's design and condition.
In evaluating a case, counsel should seek answers to the following questions.
* Was an inadvertent and rapid propelling of the carriage toward the operator a factor in the incident?
* What safety features did the saw have? What condition were they in?
* Would the presence of one or more of the safety features described above but lacking on the saw in question have substantially reduced the probability and severity of the injury?
The answers to these questions will provide guidance on the central issue in this and all products cases: Did the manufacturer place into the stream of commerce an unreasonably dangerous product not fit for its intended purpose? Or state the question in safety engineering terms. Did the manufacturer, in designing the product, do all it reasonably could to protect the user from foreseeable exposure to injury?
In a pending case in northern Virginia, a 32-year-old employee of a custom drape manufacturing shop was using a 10-inch radial arm saw in the cross-cut mode to saw half-inch-thick plywood.(8) He completed a cut and moved the carriage to the rear.
He released the saw handle and was using both hands to shift the position of the wood when the edge of the plywood bumped the still-rotating blade. The carriage was propelled rapidly toward the worker, whose right hand was struck by the blade and severely injured.
The worker alleged that the tool was defective and unreasonably dangerous because it lacked
* a trigger switch that would turn the saw off when the handle was released,
* an electronic brake to prevent prolonged coasting of the blade once power was removed,
* a a speed-control device to prevent rapid propulsion of the carriage toward the operator of the saw, and
* prominent warnings alerting users to the flyback danger and instructing them on how to avoid it.
The worker also alleged that these deficiencies consitituted a violation of an implied warranty that the saw was fit for the purpose for which it was designed, manufactured, and sold.
This case presents interesting issues. For example, some of the missing safety measures were developed after the saw was manufactured and were not available for incorporation as original equipment. On the other hand, the manufacturer made no attempt to inform owners of the availability of the improved, much safer technology or to recall and retrofit the saw with these important safety features.
What Needs to Be Done?
It is extremely important that manufacturers of radial arm saws incorporate one or more of the available safety features into saws currently in production. They should also make retrofit kits available whenever possible for saws already in use and notify owners about them.
The lack of mandatory safety standards is also a matter of concern. It appears that the nonbinding standard applicable to radial arm saws was developed more for the convenience of the manufacturer than for the safety of the user. It will be interesting to note how new editions of the so-called standard will deal with the recommendations for safety features described in this article.
In the absence of standards, successfull litigation against manufacturers may prove to be a strong incentive for saw manufacturers to add safety features. Until they do, the radial arm saw will continue to inflict serious injuries.
(1) Sears Craftsman Model 19632N Radial Arm Saw; Sears Retro-fit Blade Guard (No. 29012). (2) Passive Differential Power Shunted Load and Speed Control Apparatus, U.S. Patent No. 5,138,920 (Aug. 18, 1992); Anti-Kick Forward Device for Power-Driven Saws, U.S. Patent No. 5,152,207 (Oct. 6, 1992). (3) Ryobi Model RA 202 8-inch Precision Bench Top Radial Arm Saw; Ryobi Control Cut Retrofit Kit (No. 4590202). (4) DAVID X. MANNERS, THE GREAT TOOL EMPORIUM 143 (1979). (5) ROGER W. CLIFFE, RADIAL ARM SAW BASICS 22-25 (1991). (6) UNDERWRITERS LABS., INC., UL 987, STANDARD FOR SAFETY STATIONARY AND FIXED ELECTRIC TOOLS (1991). (7) CPSC Walk-Behind Rotary, Power Mower Controls, 16 C.F.R. [sections] 1205.5 (1993). (8) Khraibani v. Emerson Elec. Co., No. 121617 (Va., Fairfax County Cir. Ct. filed Feb. 5, 1993).
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|Title Annotation:||Products Liability|
|Author:||Kalin, Stanley R.|
|Date:||Nov 1, 1994|
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