Public exposure to significantly elevated levels of particulate matter as a result of major fires at industrial sites is a worldwide problem. Our paper describes how the United Kingdom developed its Air Quality in Major Incidents (AQinMI) service to provide fire emission plume concentration data for use by managers at the time of the incident and allow an informed public health response. It is one of the first civilian services of its type anywhere in the world. Based on the involvement of several of the authors in the AQinMI service, we describe the service’s function, detail the nature of fires covered by the service, and report for the first time on the concentrations ranges of particulate matter (PM) to which populations may be exposed in major incident fires. We also consider the human health impacts of short-term exposure to significantly elevated particulate matter concentrations and reflect on the appropriateness of current short-term guideline values in providing public health advice. We have analysed monitoring data for airborne PM (≤ 10 µm, PM10; ≤ 2.5 µm PM2.5 and ≤ 1.0 µm PM1) collected by AQinMI teams using an OSIRIS laser light scattering monitor, the UK Environment Agency’s ‘indicative standard’ equipment, during deployment to 23 major incident industrial fires. In this context, ‘indicative’ is applied to monitoring equipment that provides confirmation of the presence of particulates and indicates a measured mass concentration value. Incident-averaged concentrations ranged from 38 to 1450 µg m-3 for PM10 and 7 to 258 µg m-3 for PM2.5. Of concern was that, for several incidents, 15-minute averaged concentrations reached more than 6,500 µg m-3 for PM10 and 650 µg m-3 for PM2.5, though such excursions tended to be of relatively short duration. In the absence of accepted very short-term (15-minutes to 1-hour) guideline values for PM10 and PM2.5, we have analysed the relationship between the 1-hour and 24-hour threshold values and whether the former can be used as a predictor of longer-term exposure. Based on this analysis, for PM10, our tentative 1-hour threshold value for use in deciding whether to close public buildings or to evacuate areas is 510 µg m-3. For PM2.5, 1-hour concentrations exceeding 350 µg m-3 might indicate longer-term exposure problems. We conclude that whilst services such as AQinMI are a positive development; there is a need to consider further the accuracy of the data provided and for the development of very short-term guideline values (i.e. minutes to hours) that responders can use to determine the appropriate public health response.