Chain saws of the above-mentioned type must have a safety brake in order to meet safety regulations for the prevention of injuries. In the event of dangerous situations such as kickback, this brake must respond and bring the saw chain to a standstill virtually instantaneously. In known motor-driven chain saws of this type, this is accomplished by providing a mechanical brake, which in the event of a dangerous condition, is automatically triggered by the kickback of the chain saw or by slippage of the operator's hand toward the saw chain guide bar.
A disadvantage of known tools of this kind is that the saw chain coasts to a stop without braking if the operating switch is released. This means that if there is a normal interruption in operation, the saw chain can continue to revolve after the tool has been set down, because the unbraked rundown time lasts between 3 and 6 seconds. This presents considerable risk of injury. The still-revolving saw chain, after the tool has been set down, can come into contact with objects that will be spun about by the kinetic energy of the saw chain or will set the tool itself in motion. This can cause unforeseen injuries, especially because the operator tends not to pay as much attention to the tool after he has shut it off and thus underestimates the danger of the still-revolving saw chain.