When strong winds blow and all goes dark, diesel-powered generators provide power where there is none.

The generators are critical to keeping systems running in big buildings during disasters, and in some of those buildings – such as hospitals – it can be a life-or-death task.

But something may already be in place that can knock the emergency systems out of commission when they are needed most.  The problem is in the tank.

Since June, U.S. refineries have only been making a cleaner-burning version of diesel fuel called Ultra Low Sulfur Diesel.

The fuel has a softer impact on the environment, but it doesn’t necessarily get along well with older engines – engines like those running the emergency generator systems.

The same additives that help the fuel burn clean can dislodge other particles, clogging the systems.

Jeff Conway of Lee Technologies said it’s already happened in Houston during system tests.

“The generator started but failed almost immediately after it started. Some did not start at all,” Conway said.

The fear is that some companies haven’t tested their systems with the new fuel, or they don’t adequately maintain the systems.  One particular area of concern is the Texas Medical Center.

“We have reviewed the standards with our outside service contractors and have implemented steps in our preventative maintenance programs to ensure appropriate safety, efficiency and performance,” John Kaiander, Senior V.P. of the Texas Medical Center said in a statement.

And that’s a good thing, because there’s no telling when disaster might strike.