Licensed Professional Engineers
Forensic Clues #5A newsletter dedicated to keeping attorneys informed of the technical side of product liability cases.
Issue 5: Vol. 1 February 2004
Table Saw Accidents
By L.D. Ryan and John L. Ryan
A recent study by a woodworking website found in a study of 262 woodworking accidents that 64% of them were due to table saws. Of these table saw accidents, 68% occurred due to physical contact with the spinning blade. The rest of the accidents occurred when the saw blade caught on the work piece instead of cutting it (kickback),and the users’ hands came into contact with the spinning saw blade.
This issue of Forensic Clues will examine table saw accidents and the design flaw that makes most table saws unsafe.
Why Accidents Happen
There are many reasons accidents occur, but there are usually some common factors. A single moment of inattention or a slight slip of the hand can have devastating effects when working with a table saw. Research has proven that even the smartest, well-trained people will make errors from time to time. When the saw operator slips, it is very easy for his or her hand to come in contact with the saw blade.
Where’s the Guard?A study of 169 saw accidents found that no guard was in place in 63% of the accidents. In most home-improvement television shows, the table saws are shown being used without any sort of guard. One of the co-authors found that table saws on the cover of wood-working magazines are even shown without a guard! Nearly all table saws come with a guard. The problem is that the standard hood type guard that all saw manufacturers use is defective and unreasonably dangerous.
Table Saw Hood Guard Defects
The guard makes normal saw operation difficult because it blocks the view and makes it more difficult to feed wood and to confirm the cut location prior to sawing. The guard also fails to keep the operator’s hand from coming into the point of operation.
A more important shortcoming of the hood type guard is the failure of the guard to prevent an operator’s hand from contacting the saw blade. Shown in Figure 1 is what really happens when the guard is in place and the sawyer slips.
Figure 1. Hood type guard lifts for boards and hands
The hands go under the guard with the board due to the ability of the guard to rise over boards (or anything else). This results in a serious injury when a hand contacts the saw blade.
Figure 2: Rubber hand lifts guard from the side
Figure 3. Results of hitting the guard at an angle
Another problem with hood guards is that it can lift up, and it can move sideways. The plastic guard when pushed sideways can contact the spinning blade, and this effectively produces shrapnel from the plastic hood. This same thing can happen when using the mitre to make an angle cut when the side force on the wood moves the guard over.
Figure 4. Board pushes guard into bladeThe standard hood type guard also cannot be used for non-through cuts such as dado (notch) and rabbet cuts (see Figure 5). The guard will have to be removed to complete these cuts. This guard does not meet standard guarding principles.
Often, users will not reattach the guard once it is off, since the guard was cumbersome to begin with, and the reattachment of the guard is often a relatively difficult operation.
Figure 5. Non-through cut hits splitter
The illusion of protection provided by table saw guards could be worse than having no guard at all, because it may give operators a false sense of protection. Many saw operators will remove the guard as soon as they get their table saw home because of these reasons. In court, it is harder to win an injury case where the table saw guard was removed, unless the defects in the guard can be clearly shown to the jury.
What do the standards say?
The ANSI 01.1-1992, 1979 and 1975 were reviewed by the authors as well as OSHA 1910.231 "Woodworking Machinery Requirements". A designer following these standards implicitly would end up with the standard hood type guard found on all table saws . The standards are simply describing what industry is currently using, the psuedo hood guard. The standards even maintain that the guard will have to be removed from time to time. This is ridiculous! The standard committees apparently believe that there is no better alternative to the hood guard. We beg to differ.
The current hood type guard is clearly deficient. A guard that keeps the sawyer’s fingers away from the blade with a built-in push mechanism and a guard that stays on the saw for any operation is being developed by Safety Engineering Resources (see in Figure 6).
Figure 6. Safety Engineering Resources’ prototype saw guard.
In the case of the table saw shown, the saw designers failed to design away the hazard, the first priority in design according to the Accident Prevention Manual. Inventors have yet to come up with a saw blade that will cut wood but not flesh. In Priority Two of the Accident Prevention Manual’s hierarchy of design, however, the designers also failed to design a guard that would protect against the possibility of hands or fingers passing under the guard from the front and coming in contact with the saw blade. Saw manufacturers cannot argue with this and often imply as much in their manuals.
The Brett Guard
The Brett-Guard in Figure 7 could prevent many accidents.
Figure 7: The Brett-Guard
The transparent guard is positioned above the work piece. If the worker’s hands slip forward for any reason the fingers cannot go under the guard like the standard hood guard. The Brett-Guard is a much more effective guard than the hood type guard. Until recently, the Brett-Guard was considered unable to fulfill OSHA standard requirements.
Figure 8: Brett Guard that protects hands
Table saw guards are defective and unreasonably dangerous because of their failure to keep the operator’s hand out of the point of operation. Manufacturers are hiding behind the OSHA standards, which only perpetuate the problem by approving the deficient hood guard on all table saws.
Coming next month in Forensic Clues. . .
Lawn Mower Accidents