Now that the Department of Homeland Security and Congress agree that more needs to be done to protect the nation’s chemical plants from terrorist attacks, the challenge is writing new laws to do so. In the past the chemical industry has favored voluntary measures. These steps have failed to protect millions of Americans from the possibly deadly consequences of chemical explosions or leaks, according to Robert Stephan, the department’s assistant secretary for infrastructure protection. Instead, mandatory measures are needed, he said at a recent hearing on the subject before the Senate’s Homeland Security and Governmental Affairs Committee.

That committee, chaired by Maine Sen. Susan Collins, will hold another hearing today to gather more information about crafting such measures.

In the meantime, evidence continues to pile up that the country’s chemical facilities remain vulnerable. In a report released this week, the Congressional Research Service warned that more than 100 plants that store large amounts of toxic chemicals are located near communities of at least 1 million people. None of those facilities is in Maine, but the state is home to 34 plants that pose some level of risk. Of those, two could affect between 100,000 and 999,999 people, five could harm 10,000 to 99,999 people and 27 posed a risk to fewer than 10,000 people.

The Congressional Research Service released lists of the number of facilities in each state but did not give specific locations or company names so as not to provide such information to potential terrorists. The plants process and store large amounts of more than 140 toxic chemicals.

In his congressional testimony, Mr. Stephan estimated that fewer than 10,000 people would be killed and 40,000 sickened in a worst-case chemical release and that only a small number of facilities have the capacity to cause widespread damage.

Given the increasing sophistication of terrorists, there is still reason for concern and for federal regulations to improve the security of such facilities. A previous report from the Congressional Research Service offers good guidance on what new legislation should look like.

Congress could mandate “hardening” of defense, such as more patrols and more fencing or other barriers. It could also require that companies use less toxic chemicals when possible, which would have the added benefit of minimizing the risk of accidental exposure as well. Both approaches have been proposed in Congress and defeated.

Although Sen. Collins expressed frustration with the administration’s lack of details about what new regulations should look like, she is pleased that they, too, are calling for new rules. The challenge now is to write them and get them passed.