The federal transport safety agency is scrapping a requirement for railways to report on smaller spills involving hazardous materials, raising questions about the quality of the accident data Ottawa collects.

The Transportation Safety Board issued new regulations on Wednesday aimed at clarifying when reports must be filed on rail and other transportation accidents and detailing how investigations should take place. The new rules toughen requirements for railways to report on derailments, making it clear for the first time that a report is expected when even a single wheel on a train leaves the tracks.

The changes come eight months after an oil-laden train jumped the tracks and exploded in the small Quebec town of Lac-Mégantic, killing 47 people.

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The train was carrying oil from the Bakken formation, which is believed to be more prone to exploding than traditional crude. The area straddles North Dakota, Saskatchewan and Manitoba.

An analysis of the new TSB rules published in the Canada Gazette indicates that railways and marine shippers will no longer be expected to report on smaller spills involving hazardous goods.

Instead, the TSB will tie reporting requirements to the federal government's Transportation of Dangerous Goods regulations, which set limits for reporting on spills of different types of dangerous goods.

For example, those regulations do not require spills of flammable liquids like crude oil to be reported if they involve less than 200 litres of a substance. The change removes a regulatory burden for railways by allowing them to choose not to report spills involving smaller quantities of hazardous goods to the federal safety agency.

A spokesman for Canadian National said the company did not ask for the change, while a spokesman for Canadian Pacific did not immediately respond to a request for comment on the matter.

In contrast to Canada, the United States requires companies to report all hazardous spills, regardless of the quantity. A spokesman for the Pipeline and Hazardous Materials Safety Administration wrote in an e-mail that the information is collected because it contributes to overall safety data and can help identify potential concerns.

"Reporting of all incidents helps to build data for analysis that may point to deficiencies in hazmat [hazardous materials] packaging materials, construction or proper use," Joe Delcambre said. "Also, some hazmat spills although small could still have great consequence to public and environmental safety."

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For certain highly dangerous goods, Transport Canada requires reporting for a spill of any quantity that "could pose a danger to public safety."

A spokesman for the TSB said the agency does not believe the new reporting rules will affect the agency's ability to do its job because the unreported spills would not be significant. And another spokesman at the agency noted that the new rules also require more detailed information from companies on spills over the reporting limit.

"The effect of this provision is that small releases of dangerous goods may no longer be reportable, if none of the other reporting criteria are met," TSB spokesman Chris Krepski said. "However, when a dangerous goods release is reportable, a more detailed list of information is required from the reporting company."

The regulations also clarify when a derailment must be reported, a change that could increase the number of reports. Previously, derailments needed to be reported only in certain conditions, which sometimes led to differences of opinion.

The rail industry says 99.997 per cent of hazardous materials shipments reach their destinations safely, and Transport Minister Lisa Raitt has cited the same figure. Asked about the origin of the number last year, Transport Canada said it is based on a departmental analysis of its own data, and information from Statistics Canada and the railway industry.

The changes to the TSB's reporting regulations are scheduled to come into effect in July.