Safety/Hazard Indices: Completion of a Unified Suite of Metrics for the Assessment of Greenness for Chemical Reactions and Synthesis Plans

An overall Safety/Hazard Index (SHI) is introduced and defined in the same way as the previously described benign index (BI) covering various environmental impacts. Following the same themes and symbolism usage found in the Workplace Hazardous Materials Information System (WHMIS) and National Fire Protection Association (NFPA) 704 code, SHI covers the following safety-hazard potentials: corrosive gas (CGP), corrosive liquid/solid (CLP), flammability (FP), oxygen balance (OBP) applied to combustion reactions and oxidation reactions, hydrogen gas generation (HGP), explosive vapour (XVP), explosive strength (XSP), impact sensitivity (ISP), risk phrase (RPP), occupational exposure limit (OELP), maximum allowable concentration (MACP), dermal absorption (DAP), and skin dose (SDP). In addition, reaction temperature hazard (RTHI) and reaction pressure hazard (RPHI) indices are defined with respect to reference ambient reaction conditions of 25 degrees C and 1 atm. All three indices vary in value between 0 and 1 to conform to the formalism of BI and other well-known material efficiency green metrics. The methodology is illustrated using single-step and multistep synthesis plans for aniline, phenol, and phenyl isocyanate. Using the best available data, the overall greenest routes for these industrially important commodity chemicals are determined with respect to material efficiency, environmental impact, and safety/hazard impact. Results are conveniently presented using radial polygon diagrams and are compared with a modified Edwards-Lawrence inherent safety index formalism.