Ballast Water Sampling and Sample Analysis for Compliance Control - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 204

Fig. 15 Elbow-shaped
sampling facility to be
installed within a straight
stretch of the ships' ballast
water line
In order to undertake an accurate measurement on the organism concentration in the ballast
water, it is recommended to install an “isokinetic” sampling facility. Isokinetic sampling is
intended for the sampling of water mixtures with secondary immiscible phases (i.e., sand or
oil) in which there are substantial density differentials. In such conditions, convergence and
divergence from sampling ports is of signifi cant concern. Since most organisms are rela-
tively neutrally buoyant, true isokinetic sampling is unnecessary. However, the mathematics
related to isokinetic sampling are deemed to be useful as a basis for describing and specify-
ing sampling geometries. Isokinetic sampling is necessary to ensure that a sample contains
the same proportions of the various fl owing constituents as the fl ow stream being sampled.
During isokinetic sampling the sampling device does not alter the profi le or velocity of the
fl owing stream at the moment or point at which the sample is separated from the main fl ow
stream. Under isokinetic conditions, the velocities of both the sample and the main fl ow are
equal at the point at which the sample is separated from the main fl ow. To achieve isokinetic
sampling conditions, a sampler is designed to separate a subsection of the total fl ow-stream
in a manner that does not encourage or discourage water entry other than that which is
otherwise in the cross-section of the sampler opening. In other words, fl ow streams in the
main fl ow of the pipe should not diverge or converge as they approach the opening of the
sampler.
Sampling facility pipes should be elbow-shaped with its opening located in the
middle of the ships' main ballast water pipe and directed towards the water fl ow in
the line (see Figs. 15 and 16 ).
Sample Handling
As addressed in the G2 Guidelines, all samples should be transported, handled and
stored under proper conditions and we recommend below how this can be achieved.