This appendix contains background technical information on the processes/plants and/or systems involved in the three incidents described in this section of the main report.
Two of the incidents (power distribution failure and MP steam main rupture) were associated with "utility systems" on the Complex whilst the FCCU fire was associated with a "process plant". An explanation of the importance of this distinction is given below.
Industrial sites such as Grangemouth often refer to two different types of activities:
Process plants(also known as processes, chemical plants, manufacturing facilities, processing facilities, units etc.). The Fluidised Catalytic Cracker Unit (FCCU) which was involved in the incident of 10th June 2000 is an example of a process plant.
Process plants are the locations where the chemicals (crude oil, petrol, diesel, gas oil etc.) are handled and where either physical processes (such as separations) and/or chemical reactions are carried out. These are often complex installations handling a variety of chemicals in different states (gaseous, liquid or solid) and at varying operating conditions (for example, high or low temperatures and pressures).
Process plants have to be carefully designed, and then operated, maintained and controlled to ensure that they operate safely since a loss of containment of the chemicals can often result in major safety and environmental consequences. For this reason process plants have many different built-in safety systems designed to prevent accidents, and/or to control and mitigate the effects of accidents should they occur.
Process plants are normally run by a dedicated team of operators who are trained specifically in the operations of the process plant, have a detailed knowledge of the layout and are trained in emergency procedures. Process plants tend to operate as discrete units during normal situations but tend to rely heavily on the provision of other services (utilities) in order to function.
Utility systems(also known as services, service systems etc.). The medium pressure (MP) steam system and the power distribution system which were involved in the incidents of 27th May and 7th June 2000 respectively are examples of utility systems.
A "utility system" refers to a basic service (such as electricity, gas, electricity, steam, water, compressed air, nitrogen etc.) which is often provided from a central location such as a power station, water treatment plant etc.
In the case of the Complex the distribution systems for utilities are not under the direct control of, and are not the responsibility of the processing plants. They are maintained by a separate group on-site which in the case of the Complex is the Central Resource Group (CRG). Liaison between processing plants and the CRG is required to ensure the smooth and efficient operation of utility systems and when modifications to utility systems are proposed. The utility systems have to be operated to cope with the changing demands of a number of different process plants on the Complex at any time.
Loss of utility supplies to processing plants can cause significant disruption to process operations (for example loss of steam for heating, water for cooling or electricity for running pumps) and for this reason there are often multiple supplies of utilities or different supply routes in order to minimise the effects of a failure in part of the utility supply system. However in the event of total failure of the utility system then unless dedicated standby facilities are available on a process plant (for example diesel generators to maintain power supplies) it may be necessary to shut down processing facilities in a controlled manner until utility supplies can be restored. In some cases this may lead to processes being interrupted part way through and the requirement to safely shut down the plant may lead to chemicals being routed to flare systems and burnt in order to reduce the potential safety hazard on the process plant. Emergency flaring of chemicals in this manner may lead to "smoky flaring" (black smoke) for a period of time.