-2- (b) At the same time, the effects of fatigue, the outcome of working a week of 51/2 shifts or more since the fall of France, are probably beginning to make themselves felt. Talking into account the conditions under which the miner works, a week of 51/2 shifts or more represents a great tax on the strength and endurance of the men. It must not be forgotten that the average age level of the industry has risen sharply since before the war as a result of the failure of the industry to attract sufficient juvenile entrants for many years and because of the withdrawal to the Forces or other industries of a high proportion of the most productive age group between 21 and 30.