There are two kinds of chemical plant shut down, i.e. planned shutdown and emergency or unplanned shutdown. An example of planned shutdown is as preparation for Turn Around or yearly preventive maintenance programs. Emergency plant shutdown can be triggered by many factors, such like electric power failure, machinery failure, instrumentation trouble and many more.
In both shutdown cases, there are safety precautions for shutdown activities of chemical plants that need to be taken into account. Such safety precautions are required to prevent potential hazards that commonly appear during plant shut down.
In fact, many people may underestimate chemical plant safety in shutdown condition. Of course there may no pumps running, no reactions occur or production process. But various potential hazards such as over pressure, fire and explosion still exist, which could present real danger to the plant and people inside it.
This article is aims to provide safety precautions for shutdown activities of chemical plants. The safety precautions inside this article will not cover all the potential hazards because each plant has different potential hazards. However, they may represent the most common potential hazards during plant shutdown.
- Release pressure that may be trapped between two closed valves or closed process equipment loops. If liquid trapped inside is decomposing and releasing gas, such as hydrogen peroxide, the condition will be worst.
- Replace flammable gas inside vessel or piping line to below its Lower Explosive Limit (LEL) with inert gas, for instance nitrogen if hot work is planned to be done surround that area.
- During normal operation there may be a leak through steam valve. Insert a blind plate to stop process heating by steam, otherwise pressure inside will build up and may create over pressure or over heating condition.
- Always measure oxygen concentration inside tank or reactor at the safe level, where a job will be conducted.
- Flammable gas concentration may zero in tank or column, but beware of nitrogen hazard, since nitrogen could make oxygen level less than safer concentration.
- Maintain nitrogen blanket for tank containing flammable liquid during plant shut down. Flammable vapor is still released.
- When pressure indication just relies on pressure gauge consider error indication. Seek another one for comparison.
- Do not just rely on pressure gauge indication to make sure zero pressure. Open all available drain or vent valves to release the remaining pressure. Beware of pressure that trapped in a dead zone.
- Bring any high temperature process to ambient. It is not only saving energy but also eliminate one hazard source. Except there is a strong requirement keeping that high temperature.
- During plant shut down period, it is usually performed many jobs in the same time. Be careful not to use same hoses or transferring pump to avoid unintended reaction. Consider material compatibility. Read the MSDS to find out material compatibility.
- There will be much flammable or combustible material spread around the plant site. Do not dispose used absorbent materials that still contain flammable liquid into trash bin.
- Utilization of temporary lines or hoses may increase in shutdown period. Dispose damaged hoses and only use good hoses with the right specifications.
- Several equipments or pipelines are designed to be used only in shutdown time. Be careful, because some part of the equipments or pipes may have been corroded and would not be able to hold certain pressure rating.
- Used drums are usually used during plant shutdown in order to recover lubrication oils, chemicals or catalysts. Use only used drums that are originally used for those chemicals or ones that have been washed and cleaned up.
- In yearly preventive maintenance period, there are not only permanent workers involved in plant shutdown activities but there will be contractor workers and temporary workers. Educate them adequately about all the potential hazards that may exist in the area where they work.
- Temporary electric connections are commonly used for driving portable pumps or exhaust blowers in shutdown time. Put extra care to avoid electric spark generation because many flammable materials exposures.
- Chemical splash and spill hazards will more likely occur during maintenance works.
The above checking points do not represent all the safety precautions for shutdown activities of chemical plants. Complete the above list based on your actual plant conditions. It had better to include them in safety inspection checklists during plant shutdown.