The design of foam systems that used high viscosity foam systems has been a challenge for the fire industry since their invention in the 1970’s, but only a small percentage of foam systems were involved. With the phasing out of FPAS containing foams, the majority of foam systems now use high viscosity foam concentrates and they can have much higher viscosities than previously.
More recently, fluorine free foam concentrates have been developed that contain solid suspensions. This further complicates the design process.
Research at Charles Darwin University aims to provide tools for improved foam system design.
Our research has identified a number of problems that were previously unrecognized.
- The foam solutions may now be very viscous, and it is unsafe to assume that they can be treated like water. Some foam solutions are yield stress fluids.
- Conventional ARAFFF and some fluorine free foam concentrates form a gel when resting in the foam tank, making it much more complex to initiate flow. The results are a significant number of pump failures in the industry.
- All high viscosity foam concentrates (so far) are yield stress fluids, so they are solid when stationary. This yield stress must be overcome to initiate flow. This has important implications through the foam system design.
- Mixing of the foam concentrate with water when proportioning can be very challenging.
- Fluid property data (rheology data) available for the foam concentrates is inadequate for foam system design.
We have some tools that can be applied to these design problems. We are developing rheological tests needed to support foam system design.
