The trouble was fatigue caused by too little sleep. After a broken night, he had to get up at 5am to go to work. ''It's potentially dangerous work but if you do things in a good way and concentrate you'll be fine,'' he said. ''That's pretty hard to do when you're really tired.''

A lot of fathers of infants are suffering fatigue, a new study shows, and it can have ramifications for workplace safety, especially for men who are doing physically demanding work or handling machinery.

The study's lead author, Gary Mellor, a senior lecturer in the school of health and human sciences at Southern Cross University, has called for employers to be more aware of and sympathetic to the fatigue experienced by men during early fatherhood and do what they can to help.

''This is secret men's business,'' he said. ''They usually keep it to themselves.''

Dr Mellor has also asked fathers to consider negotiating different ways of taking leave - a week or two taken straight after the birth is not necessarily the best option because fatigue worsens over time.

The study of 241 fathers was taken at two points during their babies' first three months and found the more fatigued they were, the less they complied with safety practices. Fathers who reported fatigue were 36 per cent more likely to have ''near misses'' at work.

The vast majority experienced broken sleep when their babies were six weeks old. On average, they were woken two to three times a night and slept 5½ hours. At 12 weeks, the fathers managed a bit more sleep yet, paradoxically, were likely to feel worse. By then, three-quarters suffered from fatigue at least ''some of the time'' compared with 65 per cent at the six-week period.

This is a dramatically higher rate than for the general population, where fatigue is a problem for 20 to 30 per cent of people, the study says.

Dr Mellor said fatigue accumulated because the men were never able to recover. ''Fathers might benefit from using leave by working fewer days a week, having later start or earlier finish times, or long weekends,'' he said.

If mothers are rolling their eyes in mock sympathy at this tale, Dr Mellor reminds them the men in the study - not a randomised sample - were working, on average, 49 hours a week. This is more than the national average of 43 hours but indicative of the long work hours of fathers facing greater financial needs.

A high proportion worked at physically demanding jobs, especially in trade construction and manufacturing.

As for notorious short sleepers, such as Kevin Rudd or Margaret Thatcher, who ran a country on much less than six hours, Dr Mellor says they are helped by an entourage and can delegate.

The findings, part of a larger study, are published in the American Journal of Men's Health.

Mr Chavez said the most difficult time was a few months after his daughter's birth, but he had not made any mistakes at work. ''I felt like going back home to bed but the bills come first,'' he said. ''I'm not the only one in the world to go through this.''