DECONTAMINATION OF BIOLOGICAL AND CHEMICAL AGENTS

The present invention related to a rapid method of decontaminating surfaces which have been exposed to biological and chemical warfare agents.

US-B-7102052 and corresponding WO-A-2005/035067 describe in detail a method of decontaminating surfaces that have been contaminated with both biological and chemical agents. The chemistry of the chemical decontamination using hydrogen peroxide vapour mixed with ammonia gas or other nitrogen containing compounds is fully explained. The advantages of the techniques described in the US Patent and the International Patent Application are said to be that the gases may be applied either from an external source to an enclosure or generated within the enclosure, that there is no residue or liquid to be removed at the end of the decontamination procedure and because it is a gaseous process no damage will occur to sensitive equipment. The disadvantage of the described process is that according to the data give in the International application decontamination of chemical agent VX takes up to 24 hours. Such a long time period is undesirable especially if a significant number of items of equipment need decontamination; any technique that may shorten this period would offer advantages especially when faced with repeated chemical and biological attacks.

This invention provides a method of rendering harmless chemical/biological warfare agents, comprising exposing the agents to an atmosphere which includes a peroxide/water vapour, and causing the peroxide vapour to condense on

surfaces exposed to the chemical/biological agents; wherein ammonia gas is included in the atmosphere which is soluble in the condensate which includes water to form ammonium hydroxide to react, in conjunction with the peroxide, against the biological/chemical agents.

It is well known that biological decontamination is faster once the hydrogen peroxide and water vapours have reached saturation and a fine layer of condensation has formed. The reason is that the number of molecules available to attack the microorganisms is much greater in the liquid phase than in the vapour phase, also in the liquid phase the contact time of each molecule with the target microorganism is much longer because of the lower kinetic energy of the molecules in the liquid state. The same argument applies to chemical decontamination, faster reactions will take place once the vapours have become saturated and condensation has formed. In an atmosphere containing water and hydrogen peroxide vapours together with ammonia gas it may be expected that once the hydrogen peroxide and water vapour have reached saturation and condensation has formed that some of the ammonia will go into solution as it is highly soluble in water thus bathing the surfaces in a mixture of hydrogen peroxide solution containing ammonia, the ideal mixture to cause biological and chemical decontamination.

The following is a description of an embodiment of the invention with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of an apparatus for producing hydrogen peroxide vapour and ammonia for condensing on a surface to be decontaminated; and

Figure 2 is a graph of a decontamination cycle.

The apparatus used in the process of this invention is based on the apparatus described and illustrated in our European Patent Publication No. 1487503.

Figure 1 of the drawings show a schematic of a hydrogen peroxide and water vapour generator with a gaseous ammonia injection into the vapour stream suitable for use inside a chamber. Air is drawn into the system through inlet (10) by a fan (11) and passes through an evaporator (12) and eventually leaves the evaporator from nozzles (13) connected to the generator by pipe (14) .

Aqueous hydrogen peroxide solution is stored in bottle (15) which is connected by a conduit (22) containing a metering pump (16) to the evaporator to control the flow of the hydrogen peroxide solution to the evaporator (12) where it is flash evaporated into the air flow through the evaporator. The evaporator is heated by a band heater (17) .

The flash evaporated hydrogen peroxide and water vapour leaves the evaporator through outlet pipe (14) mixing with the air flow from the fan (11) .

Ammonia gas is stored under pressure in a cylinder (18) and released through a pressure control valve (19) and a flow control valve (20) in conduit (21) and then to outlet pipe (14) where it mixes with the hydrogen peroxide and water vapours from the evaporator (12) . The mixture of hydrogen peroxide vapour, water vapour, ammonia gas and air leave the generator through the nozzles (13) .

The whole process is controlled from a central controller which monitors and adjusts the air flow, rate of evaporation of the aqueous solution of hydrogen peroxide solution and the addition of the ammonia gas. Sensors are provided to measure the hydrogen peroxide vapour and ammonia gas concentration so that the metering pump (16) and the valve (20) can bring the vapour and gas concentration to the correct level within the chamber.

One cycle for a 300 litre chamber at 20 ⁰ C and 50% RH is illustrated in the accompanying graph of Figure 2 and has the following sequence:

• An initial injection of 15ml of vaporised 30% Hydrogen Peroxide - this was enough to produce micro-condensate on the surfaces under the prevailing conditions

• Thirty minutes after the injection phase, 3.2 standard litres of ammonia (1.61 over a two minute period) is injected into the chamber • After a further thirty minutes the chamber is aerated and the decontamination is complete.

After thirty minutes complete deactivation has been repeatedly demonstrated. SCCM on the graph refers to Standard Cubic Centimetres per Minute and PPM refers to Parts per Million Volume.

In the above cycle ammonia is injected after condensation of hydrogen peroxide. It is also possible to inject the ammonia into the chamber with the hydrogen peroxide, that is before condensation of the peroxide has taken place.