Chemical incidents can happen anytime, anywhere and when they do happen it is imperative that a public health rapid risk assessment (RRA) is undertaken to assess the risks and their potential impacts. RRAs are usually undertaken by a team of expert risk assessors with the relevant expertise for the event in question as soon as an incident occurs. The focus of this RRA will depend on the purpose of the assessment and the questions that need to be answered and will consist of four main parts: (i) hazard assessment: identification and characterisation of the hazard; (ii) exposure assessment e.g. identification of the population at risk; (iii) risk characterisation: estimation of likelihood and consequences of the risks; and (iv) context assessment: evaluating the environment in which the incident takes place. Once the risks have been identified and characterised, the RRA can be used to help inform risk mitigation actions that can reduce the level of risk to the population.