A disproportionate share of process safety incidents occurs during non-routine work: modifications, equipment replacement, tie-ins, start-up and commissioning. This study develops a quantified process safety framework for such work and applies it to a representative 28-activity brownfield project that replaces a separator, hot-taps a new compressor into a live header and upgrades a safety instrumented system. Each activity’s hazard rate is combined with the failure probabilities of its barriers. These probabilities rise with the number of simultaneous high-risk tasks and with proximity to live plant. Five framework elements were evaluated alone and in all 32 combinations: isolation management, risk-based permit to work, enhanced pre-startup review, safety instrumented system bypass management with start-up alarm rationalization, and contractor competence assurance. Inputs are representative literature values, not project data. Commissioning and start-up carried 61 percent of baseline risk, and start-up with bypassed protection alone carried 51 percent. Bypass management with alarm rationalization cut fatality-equivalent risk by 58 percent at a net saving. Four low-cost elements together cut it by 78 percent at roughly zero net cost after avoided incident costs. Adding all five reached 80 percent and reduced peak daily risk by 92 percent. Risk-aware scheduling added only 2 to 4 percent at the assumed concurrency effect, but 24 percent when that effect was quadrupled. Bypass management ranked first in 93 percent of uncertainty samples.