Introduction of the ISO 14001 to the disaster recovery – part 7/8.
Extinguishing tank fire – outline of the task
In the northern provinces of Canada, oil pipelines run in a length of several thousands of kilometers in uninhabited areas. The pump stations that convey the oil operate without an operator, under remote supervision. Buffer storage sites have been built next to the pump stations; they are used as strategic stores on the one part, and serve to equate the varying oil reception capacity of the pipeline terminal on the other. In the case of maintenance, repair or technological change-over, oil is moved to these buffer stores with a capacity of a few hundred thousands of cubic meters. These stocks are drawn when there is greater demand.
These unmanned sites have no infrastructure at all. The environmental temperature is far below zero in most part of the year, the technical equipment of the plant are designed for –40 °C. The nearest fire service is at a distance of several hundreds of kilometers, but could not help anyway without water and appropriate technology. Extinguishing tank fire – the mission impossible.
Until now, no cost-effective solution was found to protect tank farms against fire. The lack of such solution increased the economic risk of the operators, and the fire authority was dissatisfied with the level of safety. The environmental authority and NGOs strongly opposed to the construction of the pipelines, and the lack of fire prevention made it even more difficult to obtain their consent. At last, they resigned themselves to the operation of the unmanned storage sites at a temperature of –40 °C, without fire prevention for the lack of water supply.
Extinguishing tank fire under these circumstances? Having understood the technical nature of the FoamFatale technology, the operator decided to request a bid for the installation of the system, that will be able extinguishing tank fire at a storage site under construction. The designer team prepared the plans for their evaluation.
In the first phase, three storage tanks with an internal floating roof will be built; one with a diameter of 49 m and two with a diameter of 36 m. Crude oil will be stored in them.
The main point of the fire prevention concept is that in a heated room, a pressure vessel will be placed in which pre-mixed foam will be stored under pressure, in the volume necessary for the safe extinguishing of the maximum potential fire surface. The foam tank will be connected to the three hydrocarbon tanks to be protected with a closed carbon steel pipeline of appropriate diameter. The foam pipes will be connected to the foam tank through pneumatically driven valves opening when receiving a signal from the fire sensor.
- The first step is to determine the foam cover thickness to be created. This value increases with the size of the fire surface, and the expected higher degree of foam destruction will be taken into account. The foam blanket thickness will be calculated with an at least 300% safety factor compared to the effective extinguishing thickness.
- The second step is to calculate the total foam volume, which is given by the multiplication of the fire surface and the foam blanket thickness.
- As the third step, we will determine the volume of the compressed foam tank necessary for storing the foam volume calculated above.
- The last step is the hydraulic dimensioning of the foam pipe in order to meet the most important criterion, namely, the upper foam introduction time limit.
- According to our specifications, at extinguishing tank fire the entire foam volume has to be introduced into the burning tank within 2 minutes or less in the case of liquids with a flash point below 52 °C and within 3 minutes or less in the case of liquids with a flash point above 52 °C. The volume flow rate of the foam, which can be calculated from this, serves as the basic data for the hydraulic dimensioning of foam pipes.
to be continued…