| Year | Hazardous to health | Not hazardous to health |
|---|---|---|
| 2004 | 0.0 | 0 |
| 2005 | -0.5 | 1.9 |
| 2006 | -1.8 | 6.5 |
| 2007 | -2.1 | 7.5 |
| 2008 | 0.1 | -0.5 |
| 2009 | -1.9 | 6.7 |
| 2010 | -1.2 | 4.2 |
| 2011 | -2.2 | 7.9 |
| 2012 | -3.4 | 12.2 |
| 2013 | -2.6 | 9.2 |
| 2014 | -2.5 | 8.7 |
| 2015 | -3.3 | 11.7 |
| 2016 | -4.1 | 14.4 |
| 2017 | -3.4 | 11.9 |
| 2018 | -4.6 | 16.4 |
| 2019 | -3.1 | 11 |
| 2020 | -1.4 | 5.1 |