Page "Air Rail Link" Paragraph 20

However, since 1988 the WHO has classified diesel emissions as " probably carcinogenic to humans " and this classification ( in part ) has led to the new tighter standards on diesel emission ( such as the Tier 4 emission standards of the ARL ).

The carcinogenic classification is based largely on studies of high occupational exposure to diesel emissions, such as in underground mining.

The WHO announcement on the change in diesel classification does not propose any changes to the WHO Air Quality Guidelines, which were used for the air quality thresholds in the 2011 Additional Review of Human Health Assessment for the ARL ( and noted to be more stringent than the guidelines used in earlier studies ).