means practicable having regard to-
| a) | the severity and scope of the hazard or risk concerned; |
| b) | the state of knowledge reasonably available concerning that hazard or risk and of any means of removing or mitigating that hazard or risk; |
| c) | the availability and suitability of means to remove or mitigate that hazard or risk; and |
| d) | the costs and the benefits of removing or mitigating that hazard or risk. |