Yup...I only had a couple of minutes to search, but this is an excerpt from Canada's version of OSHA:

"Many conditions can lead to fatigue. For example, fatigue resulting from long hours of work and a shorter length of time between work shifts is an important concern for the health and safety of workers on extended workdays. Some researchers report that in many cases the extended workday is more tiring than the eight-hour day. They often argue that workers will be too tired by the end of ten or twelve hours and jeopardize their own well-being, and also the safety of others on the job."

Here's the link to the full report:

OSH Answers: Extended Workday: Health & Safety Issues

Carl