COSHH Essentials is a system of workplace risk management developed by the UK Health and Safety Executive for use by proprietors of small and medium sized enterprises. COSHH Essentials recommends exposure control approaches based on a chemical's potential health hazards, scale of use and ability to become airborne. More specifically, chemicals are grouped into hazard bands based on their potential health hazards, and each hazard band is associated with a 10-fold range of 8 h time weighted average airborne concentrations, termed exposure bands. The recommended control approaches are intended to limit air concentrations to within or below the exposure bands. Using air monitoring data from NIOSH Health Hazard Evaluations and Control Technology Assessments, we evaluated the ability of COSHH Essentials to select adequate control technology for vapor degreasing and bag filling operations, and the ability of the recommended control approaches to successfully limit air concentrations. We identified two types of misclassification errors. 'Under-controlled' errors were instances in which the airborne concentration exceeded the upper limit of the chemical's exposure band in the presence of control technology; such errors were observed in 78% (139/179) and 48% (76/159) of measurements collected at vapor degreasing and bag filling operations, respectively. 'Over-controlled' errors were instances in which the airborne concentration was within or below the chemical's exposure band in the absence of control technology, although conditions of use prompt COSHH Essentials to recommend controls; such errors were observed in 61% (102/167) and 8% (3/26) of measurements collected at vapor degreasing and bag filling operations, respectively. In our use of COSHH Essentials, we found that for many particulate substances toxicological information was difficult to obtain. Given the high prevalence of the control errors, we judge it is important that COSHH Essentials provide the exposure bands and information on the evaluation of control technology performance to users. In addition, we identify a number of questions for further research and outline a prospective study, which will systematically describe how small business owners use COSHH Essentials, and the frequency of under-controlled errors in practice.