## 2 Materials and Methods  
The project was undertaken during 2020/2021 and despite the impact of the COVID-19 pandemic on workplace recruitment and engagement, six workplaces were recruited to pilot/trial draft versions of the CHAP-Risk tool. Members of the Workplace Health and Safety Committee's (WHSCs) from each company received a letter outlining the project and provided consent. As a note, under our OHS legislation, these WHSCs are referred to as Joint Health and Safety Committees as they consist of representatives of both the employer and workers. These representatives are workers or supervisors from various departments within the workplace and are required to undergo basic OHS training. For the CHAP-Risk tool to be useful for our target audience (i.e., members of each company's WHSC), it was important that the intended users be involved in the development process and ultimately find the tool to be useful for their workplace context. 'User Centered Design' (UCD) is an approach for developing applications and incorporates user-centered activities throughout the entire development process [15]. The UCD approach allows end-users to influence how a design takes shape to increase its ultimate usability [16]. For the development of CHAP-Risk, we adopted a UCD approach that was informed by the following guiding principles: (a) focus on users and tasks early and throughout the design process; (b) measure usability empirically; and (c) design and test usability iteratively [17]. The eight steps in the development process are outlined in Figure 1 and described as follows:  
**Project Reference Group (Step 1):** a Project Reference Group (PRG) was formed in October 2020 to provide overall guidance for this project, including review and feedback on various versions of the CHAP-Risk tool. The group included representatives from three unions, three health and safety associations, and other researchers from three Canadian provinces (Ontario, Alberta and British Columbia). **Develop a trial version of the CHAP-Risk tool (Step 2a):** the development process for the tool was informed by engaging with the PRG and other key experts, undertaking a detailed review and evaluation of existing tools, producing a trial version of the tool, and validating this against existing tools. As it was critical that the CHAP-Risk tool be 'useful' to SMWs, the 'useability' (including aspects of effectiveness, efficiency and user satisfaction) and 'utility' (does the product help users achieve their goal) of the tool were key considerations in its design [18,19]. After an extensive literature search, the following tools were evaluated in terms of usefulness and utility: eCHAP-Basic and eCHAP-Advanced [8] which are based on the work of [PERSON] et al. [20], COSHH Essentials [21], Stoffenmanager [22], Kemi-Arvi [23], PRIO [24], NIOSH Occupational Exposure Banding e-Tool [25], and the International Chemical Control Kit [26]. Based on this evaluation, it was determined that CHAP-Risk would follow the 'hazard assessment' approaches of the eCHAP-Basic tool [8], with the 'exposure assessment', 'risk assessment' and 'control recommendation' sections informed by the approaches used by COSHH essentials [21]. For each chemical assessed, the hazard assessment step used a 'hazard banding' approach [8,20] to develop a 'hazard level' based on 'hazard statements' in Section 2 of the chemical's SDS. The exposure assessment step produced an 'exposure level' based on how the chemical was used, including its state (i.e., liquid or solid) and specific properties (i.e., operating temperature and boiling point to determine volatility for liquids, or 'dustiness' for solids), the quantity used and the frequency of use. The hazard level and exposure level were then combined in a risk matrix to determine a 'risk level' for the use of the chemical and this then had an associated 'control' recommendation.