GB2258729A - Drift indicator - Google Patents

Abstract

An atmospheric drift indicator comprising a sensitised test layer having a plurality of test areas, manually operable means for exposing each of the test areas in turn and manually operable means for masking the test areas after exposure. Preferably the exposing means is defined by the masking means. Indicator can be used to test efficiency of cooling tower drift eliminators.

Description

TITLE: DRIFT INDICATOR DESCRIPTION: The invention relates to a device intended more particularly, but not exclusively, for testing the efficiency of cooling tower drift eliminators.

Atmospheric drift, that is small liquid particles entrained in a gaseous medium, e.g. water particles in air, is emitted from devices such as cooling towers. As drift particles may contain micro-organisms such as Lesionella Dneumophila ,as well as harmful water treatment chemicals, it is important to be able to monitor the efficiency of drift eliminators.

One known method, British Standards Specification 4485 Part 2, gives a test method for "Guidance on Precipitation Rates and Determination of Droplet Size" using treated Whatman No. 1 filter paper discs on which impinging water droplets become apparent as bright blue blots. These discs are placed on the ground in the area subjected to drift nuisance. The diameter of the blots registered on the paper is then accurately measured and a detailed count is made of the numbers of blots according to diameter. Curves and tables exist within the specification for assessing the precipitation per hour over an area 100m3.

There are many variations on this type of test. One method is to clamp the disc in a traversing arm, the speed of which can be varied. Normally sampling is carried out at a height of 50mm above a pre-determined area of the drift eliminator for specific periods of time. However, sampling could be carried out at any height and in any position within a pre-determined area where drift could be anticipated to be present.

I believe that because Legionella pneumophila organisms are contained within droplets of water, the physical characteristics of the drift particles are important and that the larger the water droplets, the greater the likelihood that they could contain microorganisms, whereas, if the drift particles are of very small size, it is not possible for these particles to contain meaningful numbers of micro-organisms. Also small droplets will probably evaporate before reaching ground level, thereby reducing the risk of a susceptible human contracting the disease by inhaling a sufficient size and quantity of infected drift particles to induce infection.

Most devices for assessing drift emission are too heavy and complicated to be operated on site, other than by trained personnel. Several days are needed to analyse the results, which usually do not reflect the true efficiency of the eliminator, during which time there could be an outbreak of Legionnaires' disease, if the cooling tower is colonized with Lesionella pneumophila. Generally, only a very small area of the drift eliminator can be sampled at one time and I have discovered that the air velocity through the eliminator can vary considerably over the surface of the drift eliminator.Efficiencies are normally quoted as a percentage of water lost from circulation which is misleading in the context of deciding whether the drift emission could constitute a health hazard since it takes no account of the drift particle size or quantity of drift particles that are present in a specified quantity of air being discharged to atmosphere. I believe that the only logical method of determining this data on site accurately and instantaneously is by carrying out a particle impactation test immediately above the drift eliminator.

It is an object of the invention to provide a simple site test device that can be used by personnel such as Environmental Health Department officers and Health and Safety Executive officers to decide immediately whether or not a cooling tower is safe to continue in operation.

Recent microbiological tests conducted by Warwick University on cooling tower drift eliminators have proved a direct correlation with the water particle impactation tests which were simultaneously carried out. Thus I believe that the particle impactation method of testing is the most appropriate for use in the field.

According to the invention there is provided an atmospheric drift indicator comprising a sensitized test layer having a plurality of test areas, manually operable means for exposing each of the test areas in turn and manually operable means for masking the test areas after exposure. Preferably the exposing means is defined by the masking means.

The masking means is preferably a transparent cover which overlies the test layer. The exposing means may be an aperture formed in the cover and through which one test area of the test layer may be exposed at a time. The masking means is preferably arranged to move relative to the test layer.

The test layer may take several shapes, Thus, it may be a disc or a rectangular strip. When the test layer is disc shaped, the masking means may be arranged to rotate relative to the test layer.

The indicator is preferably mounted in a folder whereby the test material is protected against exposure before and after the test. Preferably the folder will contain a printed questionnaire in which details of the site and conditions may be recorded by the user, printed instructions as to the test method and illustrations of typical results. Preferably there will also be included a numbered grid for use in indicating the manner in which the cooling tower air outlet has been divided to correspond with the drift sampling positions. As an alternative, a space may be provided to write within the grid, to give varying durations of test, etc.

The invention is diagrammatically illustrated, by way of example, in the accompanying drawing in which: Figure 1 is a front view of an atmospheric drift indicator of the invention.

The drawing shows a drift indicator comprising a test disc 5 of chemically treated Whatman No. 1 filter paper.

A transparent acetate film cover disc 6 of the same, or slightly larger size, as compared with the test disc, is fitted over the test disc with a central fixing stud 7 which permits the acetate disc to revolve relatively to the indicator disc. The acetate disc has a cut-out segmental window 8, radiating from the central fixing device and extending over approximately one sixth of the circumference of the disc and terminating just inside the outer edge of the disc to leave a narrow margin.

The surface of the treated indicator paper is marked with six correspondingly shaped segments 5a to 5f respectively, numbered 1 to 6 to indicate the position of the window for each test. The acetate cover disc acts as a mask, the solid portion of which protects each test result after exposure.

Below the indicator disc are given four representative examples of varying drift patterns marked, A,B,C and D.

The method of testing is as follows: 1. Turn the transparent cover disc until the cut-out is opposite segment No. 1 on the indicator disc.

2. Hold the indicator at arm's length, face down, approximately 50mm above the surface of the pre designated area of the drift eliminator to be tested.

3. Hold in this position for approximately 30 seconds and then examine the indicator segment.

4. If any blue blots are apparent they should be matched with the approximate number and size of blots shown as A B C and D below the indicator.

If no blots are apparent, move the cut-out to segment No. 2, this time exposing the indicator segment for one minute.

5. Repeat steps 1 to 4, exposing the indicator in increasing steps of 30 seconds up to a maximum of two minutes.

6. If, after two minutes there are no blots visible, segment No. 6 should be used to test the viability of the reagent by applying several very small droplets of water to the exposed area of the indicator disc which should appear as bright blue blots.

The drift indicator may be mounted in a folder which contains a printed questionnaire to record details of the site and conditions, instructions as to the test method and illustrations of typical results.

The invention thus provides a simple and effective test device for measuring the efficiency of a cooling tower drift eliminator, which quickly provides an indication of the safety of the cooling tower from the point of view of potential airborne microbial or chemical contamination.

Although the test device described in the foregoing description is stated as being for use in testing the drift from a cooling tower, it will be appreciated that the device can also be used to test for the quantity and size of airborne or gasborne water or other liquid droplets in other situations, e.g. in testing the drift from a wet fume scrubber or the like.

Claims (12)

1. An atmospheric drift indicator comprising a sensitised test layer having a plurality of test areas, manually operable means for exposing each of the test areas in turn and manually operable means for masking the test areas after exposure.

2. An atmospheric drift indicator according to claim 1, wherein the exposing means is defined by the masking means.

3. An atmospheric drift indicator according to claim 1 or claim 2, wherein the masking means comprises a transparent cover which overlies the test layer.

4. An atmospheric drift indicator according to claim 3, wherein the exposing means is an aperture in the cover.

5. An atmospheric drift indicator according to any preceding claim, wherein the masking means is adapted to move relative to the test layer.

6. An atmospheric drift indicator according to any preceding claim, wherein the test layer is in the form of a disc.

7. An atmospheric drift indicator according to claim 6 when dependent on claim 5, wherein the masking means is adapted to rotate relative to the test layer.

8. An atmospheric drift indicator according to any preceding claim, wherein the test layer comprises treated paper.

9. An atmospheric drift indicator according to claim 8 when dependent on claim 7, comprising a disc shaped test paper formed with substantially sector shaped test areas, a disc shaped masking means in the form of a transparent cover rotatably mounted on the test paper and adapted to rotate concentrically with respect to the test paper, and exposing means comprising a sector shaped aperture in the cover.

10. An atmospheric drift indicator according to any preceding claim, mounted in a folder to shield it before and after testing.

11. An atmospheric drift indicator according to claim 10, wherein the folder contains information regarding the test method.

12. An atmospheric drift indicator substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.