This guidebook is carried in the cars and trucks of police, firefighters, and paramedics from the U.S., Canada, and Mexico.  Many advanced CERTs also carry this.  It helps first responders identify what hazardous material spilled - based on the placard system.  First responders can then on the spot without need of further specialists or technology, calculate the plume.  From their plume model, they can then determine where to establish a perimeter and where to evacuate as they await a haz mat squad to respond.