Hormoconis resinae in Aviation Kerosene

Micro organisms can grow in certain fuels by using the alkanes in the fuel as a foodstuff. In some cases, they may be able to utilise some of the additives in the fuel. Mid to light distillate fuels are particularly susceptible to contamination by micro-organisms, although more recently there are increasing reports of gasoline being affected, particularly some of the more “environmentally friendly” products.

The type of organisms and the damage inflicted depend upon on the fuel and the additives. All contamination is important when considering the quality of a fuel, particularly when monitoring stored products and reserves.

A wide range of micro-organisms can be found in fuels in aircraft tanks and, if left unchecked, can cause damage to the tanks, the most serious organism is the filamentous fungus H. res.

This is for a number of reasons;

 

Blockage Problems
Firstly, its size and bulk. When compared to single cell yeasts and moulds, H. res.produces far more biomass and is thus more likely to cause blockage problems.

Corrosion In Aircraft Tanks
Secondly, it is by far the most common cause of microbial corrosion in aircraft tanks. Other organisms are more important in other circumstances, for example, in some ship fuels and in long-term storage. Other important corrosive organisms are the anaerobic bacteria, collectively known as Sulphate Reducing Bacteria (SRB) or, more accurately, Sulphide Generating Bacteria (SGB). These are not common in aircraft wing tanks because of the high level of aeration produced during flight and refuelling. Other filamentous fungi may be emerging as important, but these tend not to occur without H. res. being present and, in any case, are not currently very common.

Fuel Quality
Thirdly, because of the way H. res. grows between fuel and water, it usually starts on small water droplets. It then covers the droplet, holding it in place, and continues its growth, actually generating more water under the mat due to its metabolism. In the process, it firmly attaches itself to the tank. Bacteria and yeasts require free water and are found, mainly, floating in the water phase. This means that they are less likely to adhere to surfaces and will, therefore, be significantly reduced at each water drain. H. res., once established, continues to multiply in situ.

In aircraft, high levels of bacteria and yeasts tend to indicate that you have picked up poor quality fuel and, as such, are useful indicators. However, this does not necessarily mean that they are causing any problem in the tank, and they will probably be significantly reduced at the next drain. High levels of H. res., however, indicate that there is, potentially, a serious problem.


Introducing FUELSTAT® resinae

Fuel testing kits currently available which involve total microbial counts simply tell us that there are micro organisms present in the fuel and that they are alive. Conidia Bioscience’s new FUELSTAT® resinae diagnostic test goes beyond this. Because it detects only active H. res., it tells us not only that the fungus is present and alive but also that it is growing and, therefore, the potential for damage is real.

 

We routinely biocide our storage tanks, what added value would FUELSTAT® offer us?
This question supposes that the system you currently operate includes draining water and then biociding the fuel in the storage tank. Draining the water from the tanks is the key basis for any control system. However, there are problems associated with routine biociding. Firstly, it involves costs in terms of manpower and the biocide itself. Next, there can be problems with warranties from the engine manufacturers if there is any doubt about the ppm levels of biocide in fuel. Routine use of biocides has risks in two areas; firstly there are health and safety considerations in the use of biocides; we suggest that its use should, therefore, be restricted to the minimum required to maintain clean fuel. Finally, unless the correct ppm level is maintained throughout the soak period, there is a danger that a resistant strain or strains of microbes will be produced. This last is the main reason why the preventative or maintenance dose has been removed from the options available to airline engineers in the new IATA Guidance Notes.

The introduction of a monitoring regime using FUELSTAT® resinae has enabled maintenance engineers to have real-time information on the state of the tank, allowing them to base decisions on any remedial actions on accurate data. No resource time or expense is wasted on unnecessary treatment or other actions. As the FUELSTAT® resinae on site fuel test requires only one sample per tank and takes 10 minutes to operate, it is a quick, accurate, and easy method to test kerosene fuel tanks effectively.


 

How many tests do we need to test our fuel tanks?
One test per tank is required in any monitoring regime. The issue for the maintenance and fuel inspection engineers is the frequency of testing. IATA recommends for aircraft that a minimum frequency is once a year. That frequency should be increased in relation to the risk. If in a high risk area that frequency could be increased to once a month. We do not advise that testing more frequently than monthly intervals is necessary. (We do offer a consultancy service to carry out these risk assessments).

 

Any other 'specialist' equipment required?
The only other items of equipment needed are the normal safety equipment (gloves etc) and the sample bottles necessary to hold the fluid. Other than that, the test is “stand-alone”.

 

Does it have any reaction with the biocides?
The basic answer to this is, “no it does not”. In an aircraft context, there should be a delay between biociding and retesting to see whether the biocide has been totally effective. This is done to ensure that all treated fuel has been consumed through the engines. This is obviously not possible in a storage tank scenario. In your circumstances we would suggest retesting a week after the biocide has been introduced into a contaminated tank. We are looking for traces of any surviving microbes, not the residue from that which has already been killed.