Safety Throttle
The engine throttle is operated by the trigger under the rear handle of the saw. Unless the lock-out switch above the rear handle is also pressed, the throttle cannot move from the idle position, and the chain will not be driven.
The safety throttle prevents the chain from being driven if the trigger is accidentally pushed by an obstruction, such as a branch in undergrowth. It also prevents throttle activation when hot-starting a saw on the ground with one boot inside the rear handle. The safety throttle is an additional layer of protection in this case, since the chainbrake should be applied before starting a saw in any context.
The pictured model has an enlarged lock-out or 'dead man' switch which, when released, also activates the chain brake, thus instantly halting the running chain as well as disengaging the throttle.
Read more about this topic: Chainsaw Safety Features
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