BOSTON (AP) _ The pressure in the natural gas pipelines prior to a series of explosions and fires in Massachusetts last week that killed one person and injured more than two dozen was 12 times higher than it should have been.

The information was contained in a letter from the state's U.S. senators to the heads of Columbia Gas, the company that serves the communities of Lawrence, Andover and North Andover, and NiSource, the parent company of Columbia Gas.

Democratic Sens. Elizabeth Warren and Edward Markey sent the letter Monday seeking answers to questions about the explosions.

The letter says according to the Pipeline and Hazardous Materials Safety Administration, ``the pressure in the system should have been around 0.5 pounds per square inch, but readings in the area reached at least 6 PSI.''