I was using Google to find a graphic image and one thing lead to another and I found this little gem:
PROPER ATTIRE IN THE EXPERIMENT HALL
Proper attire for work in the experiment hall includes closed-toes, covered-heel shoes and long pants. Sandals are not acceptable. Skirts may be worn if a lab coat is also worn.
Given that lab coats usually end at about the top of the knee this can’t be because they don’t want your legs showing or because they want to protect your shins from biohazards. So maybe it’s okay to spill chemicals on your pants but not on your skirt? Because this is a uni-sex environment?
What do you think?
21st-century-mom.com 
Welcome to the wonderful world of lab attire protocols that don’t make sense. Our requirements are that we must wear closed-toed shoes (open backs are OK). We must wear a lab jacket at all times, regardless of what we have on underneath. Shorts and skirts are allowed. The only thing that I can think of regarding the skirt issue is that skirts may rest above the knee when sitting down. Since many people sit at the bench, a lab coat would protect exposed skin between the knee and the top of the skirt. I’m not sure if there is a gender issue here since labs and researchers don’t usually make the dress code requirements. There is a safety office that evaluates potential hazards and, in turn, develops safety protocols. When that rule was made, it may have been possible that men did not wear shorts. My arguement has always been that it’s way easier to flush exposed skin with water than to strip off your clothes after a chemical spill–they don’t listen to me, though;) The concept is to minimize how much bare skin is exposed, but chemicals soak through clothing (and lab coats) so you have to remove the clothing and hose down after an accident anyways. Blah.Sadly, a girl lost two toes last year because she dropped a table on her foot–she was wearing open-toed shoes.