5
8
A.2
Heavy and residual fuels and oils.
A.2.1 Immediately prior to testing, shake the sample for 30 seconds.
A.2.2 Remove the cap of the MicrobMonitor2
test bottle and place it on a clean surface.
A.2.3 Open the peel pack containing a loop dispenser and remove it taking care not to touch the loop end and the
lower part of the handle.
A.2.4 Immerse the loop end into the fuel/oil to approximately 3 cm below the surface of the sample or, if there is less than 6
cm depth of fuel/oil phase, to halfway down the fuel/oil phase. Remove the loop from the sample and allow surplus fuel/oil
to drain off; ensure a film of fuel/oil is trapped within the loop.
A.2.5 Insert the loop into the neck of the MicrobMonitor2
test bottle and stab it into the gel and agitate it briefly to transfer
the sample.
A.2.6 Replace the cap on the MicrobMonitor2
bottle and tighten. Record the sample details and test date on the label
provided and stick it on a narrow side of the bottle. Proceed to step B.
A.3
Water phase associated with fuel/oil.
A.3.1 If a test of water phase is required, allow the sample to stand until free water has settled to the bottom of the sample. It
is recommended the water phase test is conducted after any fuel/oil phase test. The test procedure is essentially the same as
described above but an appropriate technique for separating/removing water from the sample needs to be used.
A.3.2 As appropriate for the volume of sample being tested (see table 1) use the loop dispenser or syringe to measure the
required volume of water.
a) To test 0.1 ml of water using the syringe;
The water phase can be drawn directly from the bottom of the sample and added to the MicrobMonitor2
test bottle. To
enable easy access to the water it may be necessary to first decant off some fuel from the sample and/or transfer the water
phase to a separate small, sterile container using a syringe or a long sterile pipette (supplied separately). Mix gently by
swirling but avoid mixing the fuel and water layers together.
Open the peel pack containing a syringe at the handle end and remove the syringe taking care not to touch the lower
barrel and nozzle. Insert the barrel of the syringe into the sample so that the nozzle is in the water phase. Draw water into
the syringe, remove from the sample and then, with the syringe nozzle uppermost, expel air. Expel surplus water until the end
of the plunger aligns with the 0.1 ml mark. Insert the tip of the syringe into the neck of the MicrobMonitor2
test bottle and
dispense the sample by fully depressing the syringe plunger. Replace the cap on the MicrobMonitor2
bottle and tighten.
Record the sample details and test date on the label provided and stick it on a narrow side of the bottle. Proceed to step
B.
b) To test 0.01 ml of water using the loop dispenser;
A syringe can be used to draw water from the bottom of the sample and then a drop of water placed into the loop and
added to the MicrobMonitor2
test bottle. Alternatively, transfer the water phase to a separate small, sterile container using a
syringe or a long sterile pipette (supplied separately). Avoid transfer of fuel. Invert the container with the separated water
three times to mix.
Remove the cap of the MicrobMonitor2
test bottle and place it on a clean surface. Open the peel pack containing a loop
dispenser and remove it taking care not to touch the loop end and the lower part of the handle. Immerse the loop end
into the separated water or fill the loop with a drop of water using a syringe. Allow surplus water to drain away but ensure the
circle of the loop remains filled with water; note, if a residue of fuel is present this can impair the ability of the loop to fill with
water. Insert the loop into the neck of the MicrobMonitor2
test bottle and stab it into the gel and agitate it briefly to transfer
the sample. Replace the cap on the MicrobMonitor2
bottle and tighten. Record the sample details and test date on the
label provided and stick it on a narrow side of the bottle. Proceed to step B.
Note The MicrobMonitor Sampling Kit (supplied separately) is a sample bottle which has a side siphon and water collection
chamber to enable easy separation of water from fuel samples.
a)
Results of test of fuel phase sample:
If 0.5 ml of fuel has been tested, multiply the number of colonies counted or estimated by 2000 to give the number of
microbial CFU per litre of fuel. If there are no colonies after the specified incubation time there are less than 2000
microbial CFU per litre of fuel.
If 0.25 ml of fuel has been tested, multiply the number of colonies counted or estimated by 4000 to give the number of
microbial CFU per litre of fuel. If there are no colonies after the specified incubation time there are less than 4000
microbial CFU per litre of fuel.
If a different volume of fuel has been tested, then a calculation can be made as follows:
Number of microbial CFU per litre = Number of colonies counted or estimated x 1000
Volume of fuel tested (ml)
b)
Results of test of water phase or oil:
If 0.1 ml of water has been tested, multiply the number of colonies counted or estimated by 10 to give the number of
microbial CFU per ml of water. If there are no colonies after the specified incubation time there are less than 10 microbial
CFU per ml of water.
If 0.01 ml of water or oil has been tested, multiply the number of colonies counted or estimated by 100 to give the number
of microbial CFU per ml of water or oil. If there are no colonies after the specified incubation time there are less than 100
microbial CFU per ml of water or oil.
If a different volume of water or oil has been tested, then a calculation can be made as follows:
Number of microbial CFU per ml = Number of colonies counted or estimated
Volume of water or oil tested (ml)
Note
If the number of colonies is too numerous to count and a sample volume of 0.5 ml or 0.25 ml of fuel or 0.1 ml or 0.01 ml
of water or oil was tested, the Test Results Chart can be used directly to determine the approximate number of
microbial CFU per litre of fuel or per ml of water or oil.
E
Calculate the number of microbial CFU in the sample.
For tests of fuel, numbers of microbes are conventionally expressed as number of CFU per litre.
For tests of water phase or oil, numbers of microbes are conventionally expressed as number of CFU per ml.
INTERPRETATION OF TEST RESULTS
There are no universally accepted limits or specifications for microbiological contamination in fuels or oils. The number of
microbial CFU which define moderate and heavy contamination levels will depend on a number of factors including the
fuel type and intended use, the sampling location, whether the sample is taken from supply and distribution facilities or
from point of end use, the intended fuel storage time and specific operational circumstances. Some guidance limits are
shown in Table 2 below. These limits are intended to provide early indication that microbial growth is occurring in the
facility sampled. Higher levels of contamination will often be required before the onset of operational problems or any
detrimental effect on fuel fitness for use. For further information see the technical guidance leaflets listed on page 2.
Table 2
Sample
Moderate
Heavy
Comment
Fuel from aircraft fuel tank drain
4000 to 20,000 CFU / litre
>20,000 CFU / litre
IATA
Contamination
Limits
Water from aircraft fuel tank drain
1000 to 10,000 CFU / ml
>10,000 CFU / ml
Bulk representative fuel sample from
supply & distribution
4000 to 20,000 CFU / litre
>20,000 CFU / ml
e.g. Aviation fuel,
diesel, marine gas
oil
Fuel from bottom / drain of supply &
distribution tank / filter
10,000 to 100,000 CFU / litre
>100,000 CFU / litre
Water phase from bottom / drain of
supply & distribution fuel tank / filter
100,000 to 1,000,000 CFU / ml
>1,000,000 CFU / ml
Lubricating / hydraulic oil in circulation
100 to 10,000 CFU / ml
>10,000 CFU / ml
Lubricating / hydraulic oil sump
1000 to 10,000 CFU / ml
>10,000 CFU / ml
MICROBMONITOR
2
®
T R U S T E D
I N N O V A T I V E
A C C U R A T E
D E P E N D A B L E
+
+
+
Results that count
