The challenge presented by general ventilation as a protective strategy is that laboratory operations use a wide variety of chemicals in changing amounts and concentrations on an irregular basis. This means that the risks associated with volatile chemicals in the laboratory change unpredictably, creating an ongoing question with regard to the design and operchallengeation of laboratory ventilation systems: How much general ventilation is required to maintain a prudent level of protection in controlling chemical hazards? In recognition of this, the ANSI Laboratory Ventilation Standard Z9.5-2012 requires the development of ‘‘an ongoing system for assessing the potential for hazardous chemical exposure’’ as a means of managing this issue.2