A yearlong Houston Chronicle investigation found that hundreds of chemicals threaten public safety across the country and in greater Houston, the capital of the nation’s petrochemical industry. Often these dangerous chemicals are stored at largely unregulated facilities that many residential neighbors don’t even know exist.

In November 2014, four people died after a gas leak at a DuPont plant. Since then, there have been 12 explosions, fires and toxic releases reported around greater Houston.

The Chronicle got chemical inventories for more than 2,500 businesses in greater Houston. They then asked chemical safety experts to rank the potential of each facility to kill or injure people and cause property or environmental damage should an incident occur. The analysis was based on the properties and quantities of the chemicals and the size of the surrounding population.