Measure
In the measuring phase of the study, one should use the tools appropriate to the nature of the operation. This article describes
the following three techniques to aid the measurement of spillage: using UV light to observe the flow pattern and leakage
points, using settling plates to observe particle decomposition, and using an air particle counter to measure spillage.
UV light. Micrometer-sized particles (< 100 µm), which cannot be observed in daylight by the human eye, can be seen easily under UV
light. The electromagnetic spectrum of UV light can be subdivided into several segments. UV light A (UVA), also called black
light, has a wavelength range of 400 to 315 nm. The energy per photon is 3.10 to 3.94 eV.
Figure 3
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The International Organization for Standardization's draft standard for determining solar irradiances (i.e., DIS-21348) states
that although black lights produce light in the UV range, their spectrum is confined to the long-wave UVA region (see Figure
3). Unlike UVB and UVC, which are responsible for the direct DNA damage that leads to skin cancer, black light is limited
to low-energy long waves and does not cause sunburn. However, UVA can damage collagen fibers and destroy vitamin A in skin
(3). Operators should take precautions to avoid direct exposure while using UV light.
A pseudostudy can be performed by using UV-fluorescent material such as the copolymer of melamine. Vitamin A and the B vitamins
thiamine, niacin, and riboflavin are strongly fluorescent. A solution made of vinegar and a crushed vitamin B-12 tablet glows
bright yellow under a black light. Melamine copolymer is water insoluble and can be detected under UV light easily because
it glows bright violet. The material should be used as a placebo, and the operation should be performed as usual. After the
UV light is turned on, the flow of the material can be observed once the mixing operation starts. Operators should record
this process with a camera so that it can be analyzed later. The operation and the critical points of spillage can be pinpointed
and recorded easily. The spillage can be caused by the operator's technique or by the equipment.
Settling plates.
Smooth, stainless-steel coupons can be used as settling plates and placed dry, wet with water, or wet with an adhesive on
previously identified critical points. After placing the plates, the mixing operation should be run as normal with a fluorescent
agent for a certain amount of time. In an operation that results in much spillage, a time of 5 min normally is sufficient,
but operations that result in light spilling can require hours or days. After the operation is finished, the plates should
be analyzed under UV light. Comparing the plates side by side helps operators identify the critical points easily (see Figures
4 and 5).
Figure 4
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Air particle counter.
The above techniques can be performed with an air particle counter probe. The probe can be placed on the critical points while
the operation is running. This placement enables operators to measure the number of particles in the air sample at a particular
point. Any air particle counter with a laser-diffraction beam can perform this study. The numbers can be recorded and analyzed
using a statistical software such as JMP (SAS, Cary, NC). Safety departments in the industry normally use the particle counter
to measure permissible exposure limits. Air particle counting can be done with a mass flow 100 particle counter (model A2408
laser particle counter, Met One Instruments, Grants Pass, OR).
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