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Consider any four of the tips for protection against unsafe system bypasses mentioned at the end of the article. Rank your choices by importance to incident prevention/risk reduction. Justify your rankings.
Chosen tips, ranked in descending order of importance:
- Report a failure or critical instrument or alarm immediately
- Carry out an MOC review before attempting to bypass a safety system.
- Follow procedures as written; take measures to fix incorrect procedures
- Use protective systems (such as interlocks) as designed
Reporting a failure immediately will trigger an appropriate response from other personnel, likely preventing subsequent failures or a potentially imminent catastrophic incident. Multiple incidents in industry have occurred because operators never reported system failures. An MOC review ensures that all process changes are accounted for, and minimizes augmented risks associated with process changes. Deviating from written procedures may have seemingly unimaginable or unlikely consequences—the written procedures have been prescribed for a reason. Finally, using protective systems such as interlocks as designed is critical since it is protecting workers and equipment from the effects of unusual conditions such as ones found during start-up, shut down, or maintenance. It prevents workers from inadvertently running the process incorrectly.
You are a chemical engineer at a plant which produces alumina via the Bayer process. Figure 1 shows a flowsheet. During the process, slurry, produced with the addition of caustic soda to bauxite, and steam, are fed into the desilicator and digesters. Electrically-powered pressure transmitter systems, designed to automatically halt the flow of steam and slurry into the vessels once the pressure has risen above a certain threshold, have been switched to manual operation to allow slurry to be forced through the units before the slurry can solidify. Otherwise, production must be halted to remove any solidified slurry from the system, against management’s wishes. Additionally, pressure relief valves were disabled during previous operations, due to leakages after previous openings.
Figure 1. Alumina production plant flowsheet
In 4-5 sentences, discuss the potential consequences of a power failure at the plant. Propose at least two measures to prevent these consequences.
Pumps and pressure control systems will fail in the event of a power outage, allowing vessel pressures to increase to dangerous levels. In the worst case scenario, a vessel could rupture, releasing caustic slurry which could injure operators. The force of the resulting explosion may also injure plant personnel. Pressure relief valves should be repaired/replaced and recommissioned; and the pressure transmitter systems should be reverted to automatic mode to limit vessel pressures. To ensure these safeguards function properly and continuously, a back-up generator must be available while the process is running. In general, safeguards against undesirable vessel pressure buildup should not be bypassed!
Research an example of a preventative safety measure commonly used in the chemical industry. Describe what it is, what it does, and why it is important.
The NFPA Safety diagram is a graphic that tells you about the chemicals in the process. It efficiently conveys the flammability, instability, and health hazards of the chemical. I think that it is important to be used because it can tell you a lot of necessary information in a very simple, easy way.