A specific sequence of events can lead to several different individual risks, each of which contributes to theoverall residual risk. For example, the re-use of a single-use device can be associated with re-infection,leaching of toxic substances, mechanical failure due to ageing and bio-incompatible disinfectant residues. Anevent tree can be a suitable method for analysing these risks. The individual residual risks need to beconsidered together to determine if the overall residual risk is acceptable.