Shutdowns of chemical plants can be dangerous, as an analysis showed accidents are five times more likely during shutdowns than normal operations. There are three types of shutdowns - normal, prolonged, and emergency - and a safety analysis must be conducted for each to prevent accidents. One way to safely manage shutdowns is through proper use of change management processes and avoiding flammable ranges when removing raw materials or finished products. A written shutdown procedure must always be used and include steps like isolating and purging lines, proving safe atmospheres, using proper personal protective equipment, and conducting pre-work meetings.

1. SHUTDOWN
The shutdown is not a routine operation and has potential dangers. A recent analysis of chemical
plants showed that an accident during the shutdown is five times more likely than normal
conditions.
The shutdowns are necessary for different reasons ranging from scheduled events to those in
emergency. So there are three categories of shutdowns:
• normal shutdown: the chemical plant is out of service in a programmed way with the aim to carry
out any maintenance, modification.
• Prolonged shutdown: the shutdown can be caused by damage to the equipment, lack of product
demand or other market reasons. The intent is to restart the system in the future.
• Emergency shutdown: a stop is not planned that can be caused by the deviation of the critical
parameters that exceed the normal limits, by an unexpected failure in equipment / machinery or
lack of utilities
It is clear that it must conduct a safety analysis for all the shutdowns to prevent any accidents.
The scheduled shutdown are determined by any requests for inspections, preventive maintenance,
equipment repair, modification process.
Generally, during a shutdown you may be required interventions such as: removal of inventory,
isolation and decontamination of containers, preparation of equipment, maintenance machines. It
may also be necessary to provide temporary piping for drainage and decontamination, cleaning
and installation of blinds and valves
One way to safely manage the shutdown is to the proper use of the change process (management
of change) .In some chemical processes an important aspect during the stop sequence is to avoid
the flammable range while removing raw products / materials finished.
One example is during the production of acrylic acid when it becomes necessary to stop the
reactor. The reactor operates with a propylene / air mixture above the upper explosive limit. Steam
is added to the reactor to maintain the contents of the reactor outside the flammability limits. The
flammability region is avoided by replacing air with steam until the mixture in the reactor is above
the flash field .Finally the steam can be taken off and the reactor is purged with air.
The decontamination managed by production is an important step in the stop procedure. This step
is operated by the production workers with special work permits, before moving the equipment
maintenance.
Normally in shutdown changes are made that must be handled with appropriate procedure.
The Flixborough accident is an example of how the installation of a temporary pipe without the
adequate support and without a safety analysis can lead to catastrophic events.
In many accidents an analysis showed that a cause basis was correct the deviation from the
application of the security procedures.
A written procedure for the stop must always be used for proper handling of requests sequences.
Below is a checklist that can be an integral part of the procedure.
1. all the lines isolated and closed
2. electrical systems locked and identified
3. Clean valves and purged
4. adequate ventilation
5. proven atmosphere
• flammable limit
• oxygen level

2. • toxic gas levels
• person in addition
6. scuba
7. A safety belt
8. Grounding
9. physical hazards
10.DPI
11.kit first aid
12.training
13. Fire-fighting equipment
14.comunication
15.signals
16.meeting before work / precautions taken
Reference
guidelines for safe process operations and maintenance-CCPS-Aiche
.