The West Fertilizer Co. fertilizer plant explosion in West, Texas killed an estimated 5 to 15 people and left more than 160 injured. Another 50-60 individuals reported to be in the vicinity of the blast are still missing.

This chemical plant, which stored anhydrous ammonia, is just one among 475 chemical plants in the United States, each of which could potentially harm more than 100,000 people in case of an accident, according to a 2012 survey conducted by the Congressional Research Service. Ninety of these could plants could endanger 1 million people or more. Check out this map of the 90 chemical plants that are in reach of the largest populations:

About the data:

Under the Clean Air Act of 1990 all chemical plants that handle regulated chemicals are required to file Risk Management Plans with the Environmental Protection Agency that outline a worst case scenario of the number of people in the plant's surrounding area that could be in harm's way if an accident occurs. The data used to create this map was compiled from these reports.

Data gathering:

While the Risk Management Plans filed with the Environmental Protection Agency are public records, individuals can only access this information at EPA reading rooms; they can retrieve a maximum of 10 reports a month involving chemical plants located anywhere in the U.S. or all the reports of the chemical plants in the area that they live in. This data was gathered by a large group of citizen researchers for the Coalition to Prevent Chemical Disasters, last updated in 2011.