The area had recently been graded, the snow was well-packed and may have been slippery. The blade had a protective pipe covering the teeth of the rake, which may have made it less stable on the sloped surface. The arms are hinged and normally do swing horizontally. Ensure that you have a safe distance between workers and potential pinch and crush points. Use tag lines or mechanical devices to guide or hold the swing arms into position prior to pinning them.
Ensure workers are aware of the hazards and know the safe work procedures.
Use these assessments to check or develop your safe work procedures.