dlweber is right. When you do your risk assessment, e/stops should never factor into the risk reduction. They're like PPE - once you've made the machine as safe as possible using elimination, substitution, engineering and administration measures, then your PPE and the e/stops are a damage limitation device should all of your actual safety measures fail. The risk of the guy getting his arm mangled by a conveyor is the same with or without an e/stop, it's just the severity of the consequences that vary.