Who said dead men tell no tales? The laboratory of the ENSA, whose role it is to train and examine guides in France, has done some tests on Dead Man (Corps Morts) anchors used for belaying where there is no suitable point. For example to rescue someone from a crevasse or to abseil onto a slope (rimaye, cornice) or to set up a running line.
If anyone has done crevasse rescue the traditional belay point is a pair of skis embedded in the snow although ski poles or even a rucksack will do. Tradition also dictates that the belay gives just at the critical moment! The test was in two parts. Looking at devices used by the rescue services then a second test looking at any object that might be available to an alpinist.
ENSA tested the following anchors: snow blocks, ice axe, ski poles, snow mushrooms and even a plastic bag filled with snow and drinks bottle. How the anchor is places can be more important than the type of anchor. The test was carried out near the Cosmiques refuge by a rock wall which was used as fixed point to attach measuring equipment.
First point to note, a dead man embedded at 25 degree to the vertical of the slope is 50% more resistant than one embedded at 90 degrees to the slope. This angle is very important. For a U shaped dead man the U should face away from the load (see video). This is counter-intuitive. They found that the plastic bag and bottle offered 250kg of resistance, enough for abseils assuming dense, neve type snow.