New Delhi, May 28 -- There are millions of chemical tanks around the U.S., and experts say it is exceedingly rare for them to fail as long as they are properly maintained and inspected.

Yet this past week, there were two major hazardous chemical emergencies on the West Coast. A large tank containing a corrosive chemical at a Longview, Washington, paper mill ruptured on Tuesday, killing two and possibly nine others. And late last week about 50,000 people were evacuated in Southern California after a chemical tank overheated and threatened the area with a catastrophic explosion. Authorities mitigated that risk, and people have been able to return home.

The incidents have raised questions about who is responsible for regulating companies t...