WW1 munitions production operations research demonstrated there was a 60 hour max. Quoting https://docs.iza.org/dp8129.pdf https://docs.iza.org/dp8129.pdf > Fr

WW1 munitions production operations research demonstrated there was a 60 hour max. Quoting https://docs.iza.org/dp8129.pdf https://docs.iza.org/dp8129.pdf > From the evidence brought to their attention, in January 1916, the HMWC recommended shorter working hours: for men, hours of no more than 65-67 per week (13-14 hours daily) on average and for boys, for girls, and for women a maximum of 60 weekly hours. It is not always clear whether these recommendations referred to scheduled hours or actual hours worked. 12 The basis for these recommendations was not because shorter hours would yield higher average product or higher marginal product, but because total output would be unchanged.