GB2295261A - Training for detection of hazardous emissions - Google Patents

Abstract

A method and apparatus is provided for training people in the detection of hazardous emissions into the atmosphere. One or more patches of a vapour-emitting composition are applied to a training site, that composition comprising a grease or paste having as vapour-forming material a relatively volatile and a relatively involatile fluorocarbon in a vehicle from which the fluorocarbons are gradually released to the atmosphere. The fluorocarbons are detected by means of a corona detector which changes its state in the presence of the fluorocarbon vapour and which is in a forced air flow to reduce the recovery time of the detector.

Description

METHOD AND APPARATUS FOR TRAINING The present invention relates to training methods which can be used to train people in the detection of hazardous emissions into the atmosphere e.g. of toxic gas from a chemical warfare agent, or poisonous chemical emissions released as a result of an industrial accident.

In such training methods, it is desirable to be able to replace the toxic gas, or poisonous chemicals by a less harmful simulant material as disclosed e.g. in UK Patent 2230126 where the simulant material is ethylene, butane or a chlorinated hydrocarbon such as chloroform which is adsorbed on molecular sieves and whose presence in air is detected by means of a portable gas detector which works by gas chromatography and flame ionisation.

However, the detector employed in this system has the disadvantage that it is non-specific for the simulant material and has a high background. It is an object of the invention to provide a detection system that does not suffer form these disadvantages and which can provide a semi-quantitative output that enables users to locate sources of airborne vapour by monitoring the concentration gradient of the vapour.

In one aspect the invention provides a detection system for training an operator in the use of a detection apparatus responsive to a first airborne vapour contaminant by the use of another detection apparatus rsponsive to a different contaminant, wherein said different contaminant is a fluorocarbon vapour or mixture of fluorocarbon vapours and said detector comprises a corona detector which changes in state in the presence of the vapour or vapours.

The invention also provides a method of training an operator in the use of a detection apparatus responsive to a first airborne vapour contaminant which comprises training the operator in the use of another detection apparatus responsive to a different contaminant, wherein said different contaminant is a fluorocarbon vapour, mixture of fluorocarbon vapours, or other electrically insulating vapour whose insulating properties are unaffected by a corona discharge, and said detector comprises a corona detector which changes in state in the presence of the vapour or vapours.

The invention also provides a detection system for an electrically insulating vapour or mixture of vapours which comprises a corona detector which changes in state in the presence of the vapour or vapours, and means for producing a forced flow of ambient air past the corona detector to reduce the hysteresis or clearance time of the detector.

The invention further provides a simulant vapour emitting composition which is a grease or paste comprising as vapour-forming materials a relatively volatile and a relatively involatile fluorocarbon in a vehicle from which the fluorocarbons are gradually released to the atmosphere.

The invention yet further provides a detector for a fluorocarbon vapour, mixture of fluorocarbon vapours, or other chemical material in vapour form which comprises a corona detector which changes in state in the presence of the vapour or vapours, and means for producing a forced flow of ambient air past the corona detector to reduce the hysteresis or clearance time of the detector.

Fluorocarbon vapour entering a corona detector in the form of a cylinder and central wire between which a corona current flows acts as an electrical insulator bringing about a small but reproducible reduction in the corona current which can be detected and employed as a signal for the presence of the vapour. However, the detector of this aspect of the invention is not limited in its response to fluorocarbon vapours, and other electrically insulating vapours which are unaffected by the corona discharge can also be detected.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 diagrammatically shows the process of simulated chemical agent detection; Figure 2 is a block diagram showing the major components of the detector used in the process of figure 1; Figure 3 is a block diagram of an electronic driving and control system forming part of the detector of figure 2; Figure 4 is a plan view of a practical form of the detector with part of its casing removed to show the working parts; Figure 5 is a diagrammatic vertical section of the detector with the casing complete; and Figure 6 is an underneath plan view similar to figure 4, but with a front part of the casing present and shown in section and with the detector removed.

Figure 1 diagrammatically shows the simulated detection of agent contamination of a location by a harmful or toxic chemical agent e.g. a nerve or blister agent which may be used in warfare or terrorist activity. A handheld battery powered detector generally indicated by the reference numeral 10 is scanned over a locus 12 having a region 14 of simulated contamination on which there is a composition having a persistent emission of a detectable airborne vapour. In practice the locus 12 may be part of a building or part of a vehicle, e.g. ship, aircraft, lorry or tank which users of the detector are being trained to decontaminate by finding the region or regions 14 and cleaning them.When the detector 10 is in close proximity to the source of the vapour, a sensing element within it responds to the vapour to produce a signal which brings about a change in the state of a visible display or in a sound generator. The requirements for the simulated detection are to show trainees how a detector operates in a real situation, to show how the region 14 can be located by following a vapour concentration gradient, to indicate the ease with which trainees can become accidentally contaminated, and to demonstrate decontamination procedures.

Chemical agents of the above type are of a persistent nature so that they are difficult to clean simply by flushing the contaminated site with water. They are usually viscous sticky materials which transfer from surface to surface on contact and are usually non- watersoluble. Each chemical agent produces a distinctive vapour profile in the neighbourhood of the contaminated locus which must be capable of being accurately reproduced in a training exercise otherwise the value of the exercise is reduced. Trainees are required to learn how to detect contamination and to clean the contaminated location by successive water flushing, scrubbing with detergent and absorption of the contaminant material into fullers earth or similar material for disposal.To permit low risk training within enclosed environments, the materials used to simulate a chemical agent must be non-explosive, non-toxic, and environmentally acceptable.

In the present invention there is employed as a simulated chemical agent a grease or paste comprising as vapourforming materials a relatively volatile and a relatively involatile fluorocarbon in a grease or paste vehicle such that the fluorocarbons are gradually released to the atmosphere. The relatively volatile material produces detectable vapour promptly after the grease or paste is applied, whereas the relatively involatile material produces sustained vapour release and prolongs the working life of the grease or paste. The vapour given off can mimic a real chemical agent in its vapour release rate and rate of drift because the vapour is heavy and clings to surfaces. The relatively volatile or low molecular weight fluorocarbon may be perfluoro 1,3dimethylcyclohezane ("Flutec" PP3, boiling pont 92-104"C, available from BNFL) and the relatively involatile or high molecular weight material may be a mixture of cis and trans- perfluorodecalins ("Flutec" PP6, boiling point 135-145"C, available from BNFL).

In one formulation the fluorocarbons are emulsified into a viscous alcohol or ether, preferably glycerol, using a high shear mixer or homogeniser to give a nominal 0.21.0 mm droplet size emulsion. It has been found that if such an emulsion is prepared immediately prior to the test and then laid down as required it has an emulsion life of 2-4 hours during which emulsified fluorocarbon persists and stable release takes place, depending upon the materials used. Another emulsifying material that may be used is polyethylene glycol, with a stabiliser being incorporated if required. Since the carrier is water-soluble the test composition can be completely and reliably removed after the end of a training session by washing down with water.

A wholly fluorocarbon system uses a perfluorocarbon oil or grease such as "Krytox" (DuPont) which is a very long chain perfluoroalkane. This formulation is best where persistence and simulated cross-contamination are required test conditions.

Representative formulations which can give a sustained and strong signal in a corona detector as described below may use low molecular weight fluorocarbon, high molecular weight fluorocarbon and a carrier or vehicle in a proportion of about 2:2:6 by weight both for the emulsions and for the fluorocarbon paste or grease mixtures. The proportions of the ingredients may, however, be varied widely depending upon the ambient conditions and the volatile materials and vehicle used and amounts of contaminant material that it is desired to simulate. However, an amount of less than 40 wt% vapour-producing fluorocarbon is not preferred because the resulting signal may not be of sufficient persistence or strength, but amounts above 40 wt% may be incorporated depending upon the properties of the emulsifying agent or fluorocarbon grease present.

The above composition may incorporate, or may be applied to the place of use in association with, a material e.g.

a high boiling point alcohol or ester which can produce a visible response on a dye-impregnated detector paper.

n-Butyl acetate is a preferred material which is of low toxicity and can produce a rapid response on test papers.

After the emulsion or grease has been applied to the required site, the n-butyl acetate may be applied over it. Alternative types of test paper may be pH paper, in which case acetic acid or another organic acid may be mixed with the emulsion or grease, or the paper detector system may be based on iodine and starch, the starch having the advantage that it can be laid down on a test paper as small dots.

The detector which is employed according to the invention subjects a corona discharge device to a current of ambient air from immediately outside the detector, the corona current decreasing in response to the presence of fluorocarbons. A control system which monitors the current through the corona device may be arranged to respond to fall of the current from a present threshold by giving an audible signal or by altering the state of a display, preferably so as to give a progressive response with current fall and hence with the amount of fluorocarbon detected. A forced flow of ambient air past the detector reduces hysteresis so that the rate of response is appropriate to an intended rate of traverse of the detector across a surface under test.For example, it is preferred that the detector current should return to its normal value within 1-2 seconds or less after removal from proximity to a source of fluorocarbons.

Referring to figure 2, the detector 10 comprises a corona sensor 15 past which a turbulent flow of ambient air is pumped by means of a pump 17, both connected to a control circuit 19 which has an in-built controller for a LCD or other display 21. The unit also has a battery power supply 23 and a normally concealed sensitivity control 25 by which the sensitivity of the detector to ambient fluorocarbon can be varied by an instructor to increase or decrease the distance from a source of fluorocarbons at which the detector will appear to saturate.

Figure 3 diagrammatically shows the control electronics.

Power from the battery 23 is supplied to the pump 17 which operates continuously and also to a blocking oscillator 27 which generates a continuous drive voltage e.g. 1.3 KV for the corona sensor 15. Current across the sensor 15 is sensed by monitor 29 whose output is fed via current-to-frequency converter 31 to a microcontroller 33 containing a stored program for controlling the various operations of the detector. The microcontroller is programmed to detect the charge in current through the sensor 15 and to supply a modified output which mimics the response of a real sensor to a real contaminant, so that for example the decay of the output signal is delayed. Change in current through the sensor 15, modified as required so as to mimic the performance of a real sensor, is displayed on an LCD 37 controlled by driver 35.The control circuit includes devices of conventional kind for battery voltage monitoring 39, power regulation 41 and reset generation 43.

Referring now to figures 4, 5 and 6, there is shown a practical form of the detector 10 which is a hand held device. A casing body generally indicated by the reference numeral 42 has integrally formed hollow handle 40 which holds the battery 23. At the front of the handle 40 on the top face of the casing there is provided a window 44 through which the LCD 37 which is of the multi-segment type can be viewed. The housing 42 has underneath the handle 40 a large compartment which receives a printed circuit board 46 on which the control electronics shown in figure 3 is supported. The pump 17 is mounted on a bulkhead 48 on the lower face of the printed circuit board 46 and receives electrical power from the circuit board 46 via power leads 50. The sensitivity control 25 appears through the rear end of the housing 42 as shown but is mounted as a sub-assembly on the circuit board 46.

The corona sensor 15 comprises a sleeve of diameter about 6 mm and length about 12 mm and has an insulating wall through which a central corona wire protrudes. The central wire and the sleeve of the detector 15 have applied between them a voltage of about 1.3 kv by means of electrical leads 52 from the circuit board 46 which lead to a contact and support block into whose forward end the detector 15 is a push fit. The detector 15 and support 54 are mounted to a bulkhead 56 which is attached to support plates 58 which also carry the printed circuit board 46 and bulkhead 48.A gas inlet nozzle 60 of plastics material has a longitudinal gas JnlL pipe which leads to an open forward end of the detector 15 and is formed with a pair of radial passages 64 which lead past the front end of the detector 15 to a small annular space 66 which is defined between the back end of the nozzle 60 and the front end of the support 54. A pipe 59 through the support 54 leads via filter 68 to the suction side of the pump 17. The return side of the pump 17 leads through air return tube 70 to discharge nozzle 72.

When the pump 17 is in operation, a flow of typically 1 litre per minute of air is drawn down the tube 62 and past but not through the detector 15 to the annular space 66 from whence it is sucked into the filter 68 and pump 17 and returns to atmosphere. The air flow in the vicinity of the forward end of the detector 15 is believed to be turbulent, so that there is rapid gasexchange between the air within the corona device 15 and the air flowing along the tube 62. Fluorocarbon contaminant or other involatile insulating material when present in the ambient air builds up in the detector 15 where it acts as an electrical insulator bringing about a fall in the corona current between the central wire and the outer sleeve of the corona device.However, when the nozzle 60 is removed from a place contaminated with fluorocarbon or other electrically insulating involatile material, the gas flow past the detector 15 rapidly flushes out contaminant present therein so that the corona current returns to its normal quiescent value typically within one to two seconds. The filter 68 is provided to protect the pump 17 which is a relatively expensive component from damage by liquid accidently picked up through the pipe 62.

In practice, the materials used for the text, namely the Flutec PP3, Flutec PP6 and Krytox are provided in individual containers from which they are withdrawn using a syringe or pipette and mixed in a mixing jar in a weight ratio of 2:2:6. The mixture has either to be used immediately or to be stored in an airtight container as the volatile PP3 and PP6 begin to evaporate as soon as they are in contact with the air. The mixture is applied in patches of about 10 ml to region of a building or ship required to have simulated contamination. A so called confidence tester" containing a predetermined dose of the mixture is also prepared.

The detector display 37 has typically 8 progressively energisable display bars which are activated one after the other to denote successive increases in fluorocarbon detected in the environment. For calibration purpose the detector is moved to a distance at which it is desired that a predetermined portion of the display should be active e.g. that 6 bars out of the 8 should be active.

A calibration control is then operated which sets the sensitivity of the detector for the density of simulation material detected. The control software then retains the detector in a rapid response state for a period of e.g.

20 seconds during which an instructor can move the detector towards and away from the contamination source used for calibration and monitor changes on the display which in this state of the control electronics is updated rapidly so that the instructor can assess whether the detector is exhibiting the desired performance. If less than a threshold number of bars on the display are active, the instructor will recalibrate the detector at a location where there is more simulant vapour present.

During calibration the instructor can set the sensitivity of the device by means of the control knob 25.

When calibration is complete, a cover is placed over the control knob 25 so that trainees cannot alter its setting. The control software then places the detector in a training mode in which the display 37 is updated relatively slowly with changes in vapour level, mimicking the performance of a typical chemical agent detector which for example when removed from a source of contamination may take 30 seconds to clear to its quiescent state. The calibration is retained by the detector when the power is turned off so that the detector may not need recalibration at every training session. If the air temperature, air flow through the detector and temperature of the simulant material remain constant then it is unlikely that recalibration of the detector will be needed, although the instructors will be recommended to check the operation of the detector before starting a training exercise.

Although the use of the detector has been described in relation to fluorocarbons or hazardous materials, it may find other uses e.g. in the tracing of sources of halocarbon contamination from a refrigeration system.

Claims (30)

1. A detection system for training an operator in the use of a detection apparatus responsive to a first airborne vapour contaminant by the use of another detection apparatus responsive to a different contaminant, wherein said different contaminant is a fluorocarbon vapour or mixture of fluorocarbon vapours and said detector comprises a corona detector which changes in state in the presence of the vapour or vapours.

2. The detection system of claim 1, wherein the simulated chemical agent is a grease or paste comprising as vapour-forming materials a relatively volatile and a relatively involatile fluorocarbon in a vehicle such that the fluorocarbons are gradually released to the atmosphere.

3. The detection system of claim 2, wherein the relatively volatile fluorocarbon boils at 90-1050C and the relatively involatile fluorocarbon boils a about 130-150"C.

4. The detection system of claim 2 or 3, wherein the chemical agent is an emulsion of the relatively volatile and the relatively involatile fluorocarbon in a viscous alcohol or ether.

5. The detection system of claim 2 or 3, wherein the chemical agent is an emulsion of the relatively volatile and the relatively involatile fluorocarbon in glycerol.

6. The detection system of claim 2 or 3, wherein the chemical agent is a mixture of the relatively volatile and the relatively involatile fluorocarbon with a fluorocarbon grease.

7. The detection system of any of claims 2-6, wherein the chemical agent comprises 40% by weight or above of the relatively volatile and the relatively involatile fluorocarbon.

8. The detection system of any preceding claim, wherein the detector includes a corona device in which an electrical potential is maintained between a wire and a sleeve surrounding the wire, and means for causing a current of ambient air from immediately outside the detector to flow past the corona device, the corona current decreasing in response to the presence of fluorocarbons.

9. The detection system of claim 8, wherein the detector has a pump which causes a forced flow of ambient air past the corona device.

10. The detection system of claim 8 or 9, wherein the detector further comprises a control system arranged to monitor the current through or voltage across the corona device and to respond to fall of the current or change in voltage from a preset threshold by giving an audible signal or by altering the state of a display.

11. The detection system of claim 10, wherein the detector has a display in which a visible response is progressive and the control system is arranged to cause progressive response of the display with corona current fall or voltage change and hence with the amount of fluorocarbon detected.

12. The detection system of any of claims 8-11, wherein the forced flow of ambient air past the detector is arranged to reduce the hysteresis of the corona device so that it returns to its quiescent response within 1-2 seconds or less after removal from proximity to a source of fluorocarbons.

13. A detection system for an electrically insulating vapour or mixture of vapours which comprises a corona detector which changes in state in the presence of the vapour or vapours, and means for producing a forced flow of ambient air past the corona detector to reduce the time the detector takes to return to its quiescent state.

14. A composition for use in training an operator in the use of a detection apparatus responsive to a first airborne vapour contaminant by the use of another detection apparatus responsive to said composition which contains a different contaminant, characterised in that the composition is a grease or paste comprising as vapour-forming materials a relatively volatile and a relatively involatile fluorocarbon in a vehicle from which the fluorocarbons are gradually released to the atmosphere.

15. The composition of claim 14, wherein the relatively volatile fluorocarbon boils at 90-1050C and the relatively involatile fluorocarbon boils at about 130-150"C.

16. The composition of claim 14 or 15, wherein the chemical agent is an emulsion of the relatively volatile and the relatively involatile fluorocarbon in a viscous alcohol or ether.

17. The composition of claim 14 or 15, wherein the chemical agent is an emulsion of the relatively volatile and the relatively involatile fluorocarbon in glycerol.

18. The composition of claim 14 or 15, wherein the chemical agent is a mixture of the relatively volatile and the relatively involatile fluorocarbon with a fluorocarbon grease.

19. The composition of any of claims 14-18, wherein he chemical agent comprises 40% by weight or above of the relatively volatile and the relatively involatile fluorocarbon.

20. The composition of any of claims 14 to 19, when in association with a material which produces a colour change in a dye-impregnated test paper.

21. The composition of any of claims 14 to 19, when in association with n-butyl acrylate.

22. A detector for a fluorocarbon vapour, mixture of fluorocarbon vapours, or other chemical material in vapour form which comprises a corona detector which changes in state in the presence of the vapour or vapours, and means for producing a forced flow of ambient air past the corona detector to reduce the recovery time of the detector.

23. The detector of claim 22, wherein the vapour to which the detector is responsive is an electrical insulator whose insulation properties are unaffected by the corona and the corona current decreases in response to the presence of fluorocarbons.

24. The detector of claim 23, which has a pump for causing a forced flow of ambient air past the corona charging device.

25. The detector of claim 23 or 24, wherein the detector further comprises a control system arranged to monitor the current through or voltage across the corona device and to respond to fall of the current or change in voltage from a present threshold by giving an audible signal or by altering the state of display.

26. The detector of claim 25, wherein there is present a display in which a visible response is progressive and the control system is arranged to cause progressive response of the display with current fall or voltage change and hence with the amount of fluorocarbon detected.

27. The detector of any of claims 22-26, wherein the forced flow of ambient air past the detector is arranged to reduce the hysteresis of the corona device so that it returns to is quiescent response within 1-2 seconds or less after removal from proximity to a source of fluorocarbon.

28. A detection system for training an operator in the use of a detection apparatus responsive to a first airborne vapour contaminant by the use of another detection apparatus responsive to a different contaminant, said system being substantially as hereinbefore described with reference to the accompanying drawings.

29. A detector for electrically insulating contaminant gases in air, substantially as hereinbefore described with reference to the accompanying drawings.

30. A method of training an operator in the use of a detection apparatus responsive to a first airborne vapour contaminant which comprises training the operator in the use of another detection apparatus responsive to a different contaminant, wherein said different contaminant is a fluorocarbon vapour, mixture of fluorocarbon vapours, or other electrically insulating vapour whose insulating properties are unaffected by a corona discharge, and said detector comprises a corona detector which changes in state in the presence of the vapour or vapours.