An 18-wheeler collided with a taxi on the Zakim northbound shortly after 5:30 a.m..
The crash and fire led police to shut both sides of the bridge; the northbound side remained completely shut until 9 a.m., when one lane was reopened.
Josh Wardell says based on the debris strewn across the bridge, the truck was carrying apples
The accident was close to the pier tower leg and in some photos you can see the soot on the concrete. Fortunately the fire was not close to the cables which could have meant the bridge needing to be closed for inspections and repairs.
Here is an article about a fire on a cable stay bridge in Mexico where cables were damaged and repairs were made.
Mezcala Bridge Fire Damage Event
The multispan stayed or cable bridge suffered damages to one of the stay cables with a minor damage to an adjoining cable during a fire that was created due to an accident on March 17, 2007 between two school buses and a truck at the middle span of the bridge. The truck was carrying coconuts, which was the reason for the fire. After closing the bridge for vehicular traffic temporarily, the cable was replaced; though traffic was partially restored when the cable replacement started. Analysis of the cause of the fire by the American Society of Civil Engineers and the China Communications and Transportation Association indicated that the High-density polyethylene (HDPE) sheathing, which has hydrocarbon composition, was not ideally fire resistant as it caught fire and created the additional fire load which resulted in snapping of one cable line. A moot question that was posed in the analysis was "would this bridge have survived the loss of two or three adjacent cables?" Analysis also showed that multiple cables could be included in a fire caused by a lightning strike.
Bridge designers have examined the lacunae in design of major long span bridges of various types in the world, keeping in view the failures that have occurred in many bridges including the limited failure of the cable of the Mezcala Bridge due to a single point loading event that occurred due to a fire. This study was done with the objective "to enhance the reliability and safety of these major structures in the built environment." The approach now under consideration for cable stayed bridge is "a more rational approach from assigning factors of safety to key elements such as suspenders and stay cables, to setting depth and stiffness requirements