Conventional technologies, reasons of low success rate
Conventional technologies apply foam with mobile, semi-fixed and fixed equipment.
Foam proportioning
The foam concentrate has to be proportioned into the water. The operating range of the proportioning equipment is always limited. The range giving an acceptable deviation from the set point is even more limited. The response of the proportioner to quick flow variations is generally speaking not very good. Proportioning systems range from very simple and not very reliable systems to electronically controlled sophisticated and complicated, but therefore also vulnerable devices.
Foam generation
To make expanded foam it is necessary to entrain air into the foam solution stream. Venturi type aspirating devices are typically used for this purpose. Proper functioning of such a device is determined by the delicate balance between flow rate, upstream pressure and backpressure. Optimum performance can only be achieved in a rather narrow operating range. Blockage or partial blockage of the small bore air inlet often occurs in fixed systems in locations where maintenance is not optimal. This results in malfunctioning.
Dependence on water
In conventional foam systems (including the CAFS too) the availability of firewater is essential. A number of steps are required to convert foam concentrate, water and air into expanded foam. The expanded foam can subsequently be applied onto the burning surface. In the majority of cases these activities take place close to the scene of the fire. Quite a team of trained manpower is required to set up these relatively complicated systems. In view of the stressful situation during any fire, mistakes are likely to be made resulting in malperformance of the system.
Unmanned storage sites cannot count on turnout of sufficient firefighters within a reasonable period of time.
Over the past decades, the user had no choice but to accept these complicated and expensive systems. Sites that had no access to adequate water were left without protection. The owners/management, the Fire Administration and the Environment Protection Authorities had no choice but to accept the situation.
Conclusion
There are sites where:
- The implementation of conventional fire protection systems is facing serious technical problems.
- The cost to set up an installation complying with NFPA recommendations is too high.
- There is insufficient manpower available at short notice to operate a labour-intensive mobile or semi-fixed system.
- There is a need for an acceptable level of reliability.
