SEATTLE — The federal Surface Transportation Board has decided that BNSF Railway can require coal shippers to use certain methods to reduce the amount of coal dust lost from rail cars leaving coal mines in Wyoming and Montana.

In a decision last Wednesday, the board said shippers challenging the railway’s coal-loading rules had not shown the measures were unreasonable. It did, however, find one provision related to liability unreasonable.

BNSF spokeswoman Courtney Wallace said Tuesday the board’s decision ensures coal dust stays in railcars where it belongs.

“We established our coal loading rule after extensive field testing, and when properly followed, our rule effectively addresses issues with coal dust,” Wallace said in a statement.

Environmental and other groups have raised concerns about coal dust escaping from railcars, as proposed port terminals in Washington and Oregon aims to ship millions tons of coal by train from the Power River Basin of Montana and Wyoming for export to Asia.

In June, the Sierra Club, Puget Soundkeeper Alliance, Columbia Riverkeeper and other environmental groups sued BNSF and several top coal producers in federal court in Seattle, alleging violations of the federal Clean Water Act. The lawsuit alleges the coal trains discharge coal, coal chunks, coal dust and other pollutants into Washington state waterways.

The groups say the coal breaks apart easily and contains mercury, arsenic, uranium, and other toxins harmful to fish and human health. The discharges occur despite the use of topping agents or other suppressants, the lawsuit alleges.

A BNSF spokesman has dismissed that lawsuit as a publicity stunt to stop coal exports from the Northwest.

BNSF says it has been working to reduce coal dust because it poses a threat to the stability of its tracks and ultimately the operation of its lines in the Powder River Basin.

In March 2011, the STB found that coal dust emissions from open-top railcars are fouling track beds, and that BNSF could take steps to suppress those emissions. But it held that BNSF’s rule created too much uncertainty.

BNSF issued new rules in July 2011 that require coal be loaded into a bread loaf shape and sprayed with one of several approved topper agents, or another alternative.

Wallace said BNSF will work with Powder River Basin shippers to ensure full compliance.

Steve Sharp, fuels director with the Arkansas Electric Cooperative Corp., one of the challengers, said Tuesday he was pleased the board struck down a provision that could have opened shippers to liability. But he said he was disappointed with the board’s decision to side with BNSF on coal-loading.

Sharp questioned whether topping agents were the cost-effective ways to control dust, and said he believed the amount of coal dust coming off railcars was much smaller than BNSF noted.