Regarding the closing of lane(s), a direction or entire highway at the scene of an MVA, Haz-Mat or fire, things can and do escalate. In 2006, in Morris County NJ on I-80 a Rockaway Twp deputy chief was arrested, transported to state pd barracks and held for two hours for failure to obey a trooper. The chauffeur was also ticketed. A link is attached below for the full story.
While I see both points as to keeping traffic flowing and the safety of emergency personnel operating, I'll add this one caveat. When the fire department or EMS is operating at a fire, MVA with injuries etc, time is of the essence for patient care/future return to health of the injured. We don't want to be on the highway any longer than necessary, but while there we don't want to become part of the original accident.
The caveat being it may be a closure of 5-15 minutes that is the low and high side of an incident. Yes, traffic backs up fast and lasts long after the scene is clear of any evidence that an MVA or fire ever occurred. If in fact an accident goes fatal or multi-fatal, the troopers will shut lanes or the highway for an extended period while an accident reconstruction team goes about their collection of evidence, photographs, and measurements.
If the incident was or becomes a crime scene, {someone tossing rocks off an overpass onto windshields below, a sniper incident, a police pursuit terminating in a crash, are but a few examples} the troopers will shut down that roadway for an extended time period. It does seem in these instances to be somewhat hypocritical what is permissible and what is refused. I applaud the IC mentioned in a prior posting that responded to a truck full of tires that was on fire when ordered to move fire equipment {which might lead to emergency personnel injury going unseen, and further MVA's as there isn't a much darker smoke that when tires are on fire} that he pulled his equipment and crews off the highway and told the trooper to put the fire out with his baton. The tires were never going to be sold, the truck was likely going to be totalled, no firefighters were injured and the trooper had his highway back, although maybe not as he wanted it.
http://forums.firehouse.com/archive/index.php/t-85761.html