There may still be some question about what caused the blast. A news report I heard this morning discussed schrapnel that looked like BBs. That doesn't sounds like the shrapnel you'd get from a manufactured rocket or mortar round. If the report is true, then it might've been a homemade rocket similar to the ones Palestineans have used against Israel, or it might've been a bomb planted inside the facility.

A concrete mess hall would provide a measure of protection against rockets and mortars. On the other hand, it would tend to contain the blast from an internal bomb, making it even more deadly. They can mitigate this risk by stepping up security to reduce the chances of a bomb making it into the facility and perhaps by including overpressure blowout panels.