Installations which make, handle and store liquid chlorine represent one of the largest groups of hazardous plants which pose high levels of risk to off-site populations. For such installations, risk analysis is one of the most important tools now being used to improve safety, by aiding decisions on the acceptability or tolerability of the risks and thereby ascertaining the need for and nature of risk reduction measures. This paper describes a study undertaken following a regulatory authority requirement to enclose a particular chlorine plant in a ＇containment＇ system. We seek to demonstrate how ＇peopleware＇ issues such as human factors, training, emergency planning procedures and so on can be properly represented in a conventional quantified risk analysis, and show how a containment system, as shown by the accurate modelling of release conditions, may not actually reduce risk to off-site populations. By giving proper credit to detection and response arrangements, procedures, training and emergency planning, aspects which most safety professionals consider to be very valuable components of a risk management strategy, we were able to design a package of measures that would produce a net risk reduction significantly better than that produced by a containment approach.