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 °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.