Nearly everyone who lives in a snowy climate would agree that a gas powered snow blower beats a person powered snow shovel for clearing the sidewalk or driveway. Shoveling heavy, wet snow causes injuries from back problems to heart attacks. No wonder that gas powered snow blowers of all sizes are a popular item this time of year. The larger ones may be ride-on types; smaller ones are typically walk-behind. In either case there is an auger to gather the snow as the device moves forward and a bladed fan (or “blower”) to discharge it out of a chute to one side or the other.
But these machines are not without hazard. Snow and ice compact easily, and the blower outlet can become packed, blocking the discharge. Manufacturers typically provide solutions to this problem. One is a simple hand-tool located conveniently for use in unclogging the blower outlet. Another is a provision of a squeeze grip “dead-man’s” switch mounted on the operator’s handle. This important safety feature is required by standards. (cf. ANSI B71.3) When squeezed and held, the machine’s auger and blower are engaged, and snow is discharged. When released, the auger and blower are de-clutched and stop rotating. The snow blower’s motor continues to run. Drive wheels are clutched and de-clutched by a similar grip on the other handle. Modern lawn mowers have a similar arrangement.
However, in an injury case that we investigated we concluded that there was a design defect that allowed the blower to keep rotating even when the handle was released, and that was the cause of the injury.
The operator was working on clearing back the piled snow near a building’s service entrance. The snow had previously been pushed aside by a truck plow, so that it was somewhat deeper and also contained compacted chunks of snow. Clearing required pushing forward into the snow pile, then pulling backward to reposition. The snow blower’s discharge chute became clogged, or packed with snow and ice. Having released both grips to move around to the front of the discharge chute, the operator believed that the auger and blower were not running. With the packed snow, he could not visibly confirm if this were so. He was wearing heavy work gloves. There was no tool provided to break up the jam. He reached into the chute to clear the jam, far enough to encounter the still rotating blower, and his fingers and hand were injured.
On this particular machine, a co-axial push-pull cable is connected to the deadman switch. This cable in turn connects to a lever linkage that converts the push-pull to a rotary motion of a steel shaft attached to a clutch. This linkage was located outside, on the back side of the machine, about eight inches above the ground. The rotating steel shaft passes through a hole in the sheet metal chassis, and connects or disconnects the motor drive to the impeller and auger. The clutch mechanism is inside the chassis.
The hazard in this incident is the rapidly rotating blades of the auger or impeller. Providing a physical guard over the inlet and outlet chutes would more likely than not prevent the machine from performing its task. So the designers therefore provided the spring grip clutch system to stop rotation if the operator released the spring grip. The design defect was that part of the mechanical linkage to disengage the impeller is outside the chassis, exposed to the potential for jamming. Snow jammed the clutch lever in the engaged position, and it remained jammed even if the spring grip on the handle was released. At inspection, it required only a small amount of force to hold the lever in the engaged position with the spring grip released.
Interestingly, in a walk behind lawn mower of similar size and power, made by the same manufacturer, the clutch lever linkages were safely inside the mower chassis.
Founded in 1997, The Warren Group, forensic engineers and consultants provides technical investigations and analysis of personal injury and property claims as well as expert testimony for insurance adjusters and attorneys. Extremely well versed in the disciplines of mechanical, electrical, chemical, structural, accident reconstruction and fire and explosion investigation, our engineers and consultants are known for delivering the truth — origin, cause, responsibility and cost of an event or claim — with unmistakable clarity.