Background of the invention Protective suits are available for a range of hazardous environments, including hazardous chemicals in liquid and vapour form. One big disadvantage for workers using protective suits is that they are generally uncomfortable. To achieve good protection, the suit must be sealed to the wearer's body and therefore offers a significant barrier to heat transfer by convection, conduction, radiation and evaporation. Consequently, the temperature and humidity may rise rapidly during work. In extreme circumstances humidity approaches 100%, the bodies'natural cooling system stops working as no water can evaporate from the skin, blood temperature increases and, if work continues, heat stress results.

Summary of the invention The invention is a ventilation system for a protective suit, including in combination: A protective suit to cover the user's body.

A face piece to cover at least the nose or mouth of the user.

A filter and pump unit to draw air from outside the protective suit and to supply breathing air to a space within the face piece and ventilating air to the interior of the protective suit.

Where, the breathing air is supplied such that the pressure inside the face piece does not drop below the pressure acting on the outside of the face piece during the breathing cycle, no matter how strenuously the user is working. To achieve this breathing air may be supplied at the expense of ventilating air during inhalation.

The protective suit may be gas tight and encapsulate the entire body of the user. The protective suit will typically comprise polyamide coated with

PVC, butyl or chloroprene rubber or polymer barrier laminate. A transparent screen is provided in front of the user's face to enable them to look out.

Alternatively, the hands and feet may be covered with gloves and boots which seal against the suit. The face may also not be covered by the suit, but only by the face piece.

The pump unit may be worn in a harness and is positioned inside the back of the protective suit where space is provided by an extension. A port is provided in the extension for air to be drawn in from outside the protective suit by the pump unit. The filter may be outside the suit and screwed to a spigot extending from the pump unit through the port. Positioning the filter outside the suit makes it easier to change. An air-tight connection is made around the port when the filter and pump are properly connected so that no air may pass through the port without passing through the filter. There may be more than one port and filter.

The pump unit includes a pump driven by an electric motor and a power pack for the motor. The SE400 unit from Safety Equipment Australia is particularly beneficial in this combination. The SE400 is a fan supplied positive pressure, breath responsive respirator able to respond to the breathing demand of the user.

An air inlet valve may be provided to prevent the return of exhaled air to the pump unit. An air outlet valve may be maintained in a closed position during inhalation solely by air pressure from the pump unit and be opened during exhalation.

This pump unit operates at a low pressure but at a relatively high flow rate. The pump unit is capable of delivering at least 150 litres of air per minute, and at rates up to and beyond 300 litres per minute or 500 litres per minute.

Exhaled air may be vented into the suit from the face piece via a non- return valve. During exhalation filtered air from the pump unit is also vented from the non-return valve to provide ventilating air to the suit. As pressure builds inside the suit air is vented out of the suit to atmosphere, via another non-return valve. Maintaining the pressure inside the suit above ambient prevents environmental contaminants from entering the suit, and from passing from the suit into the face piece.

In an alternative, exhaled air may be vented directly out of the suit, in which case a separate circuit is provided for the ventilating air. The

ventilating circuit may deliver ventilating air into the back of the suit, to the transparent screen to ensure it does not become misted, or along conduits to the extremities of the arms and legs of the suit.

A ventilation valve may be provided for ventilation flow adjuistment, and it may be manually or automatically activated. Sensors may be provided to measure temperature or humidity, or both, inside the protective suit. The pump unit may be equipped with sensors to measure the pressure inside the suit as well as inside the face piece. The output of such sensors may be used to control the ventilation airflow automatically, either by controlling the pump unit, or the ventilation valve.

An inlet valve may be provided to control the inlet of air to the pump and filter unit. The inlet valve may be arranged upstream or downstream of the fan to close when a defined air pressure is present within the pump unit.

With this valve it is easier to ensure that there is always a positive pressure within the face piece at all times, and so avoid a negative pressure which could give rise to the entry of contaminated air.

Filters may be employed in the filter and pump unit for purifying the breathing air, and the ventilating air.

The term filter is taken to include any device for the removal of particulate or gaseous contaminants from the inhaled air. The particulates may be solid, as in smoke, or liquid as in insecticide sprays. The filter may be adapted to remove gaseous contaminants, in which case the filter may be in the form of activated carbon or another gaseous absorbent. Also a filter may be used to filter the exhalation air when in a decontamination room to keep the room uncontaminated.

For different applications of the breathing apparatus, different filter types are employed. Each different type of filter alters the flow resistance.

The demands placed on the pump unit will also vary with each filter type as a filter is progressively used. It has been found that calibrating the pump unit prior to use such that the speed and rotation of the fan is set at an optimum base value, results in a saving of power and an increase in filter life.

The apparatus may include an electronic data processor to monitor and controls the speed of the motor so as to ensure adequate air flow to the face piece. The processor may take account of the filter type and flow resistance

to set the optimum value of speed of rotation of the fan. The processor may also use the results obtained by the sensors.

A device for drying the ventilating air may be provided, as may a device for cooling the ventilating air.

In a further aspect the invention is a gas tight protective suit to cover a user's body, comprising: A rear extension to house a pump unit worn in a harness, and a port in the extension for air to be drawn in from outside the protective suit by a pump unit. An air-tight connection being made around the port when a filter is properly connected to the pump unit so that no air may pass through the port without passing through the filter. There may be more than one port and filter.

The protective suit may be gas tight and encapsulate the entire body of the user. The protective suit will typically comprise polyamide coated with PVC, butyl or chloroprene rubber or polymer barrier laminate. A transparent screen is provided in front of the user's face to enable them to look out.

Brief Description of the Drawings Examples of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a pictorial diagram of a protective suit embodying the invention.

Figure 2 is a pictorial diagram of an alternative protective suit embodying the invention.

Figure 3 is a pictorial diagram of a second alternative protective suit embodying the invention.

Figure 4 is a pictorial diagram of a third alternative protective suit embodying the invention.

Figure 5 is a pictorial diagram of a fourth alternative protective suit embodying the invention.

Figure 6a is a graph of the flow of breathing air; Figure 6b is a graph of the flow of ventilating air; and Figure 6c is a graph of the total flow of air.

Detailed description of the drawings Referring to Figure 1, user 1 is wearing a gas tight polyamide protective suit 2. Boots 3 are sealed to the suit around the ankles, and gloves 4 around

the wrists to provide complete protection from the environment. A transparent panel of chemical resistant PVC 5 allows the user to view the environment. An extension 6 of the suit covers a pump unit 7.

Inside the suit 2, the user wears a harness 8 to mount the pump unit 7 on his back. A hole 9 in the back of the suit provides an air inlet port for the pump unit to take atmospheric air from the environment. A filter 10 connects to the pump unit and seals hole 8 to prevent ingress of atmospheric gases into the suit. To do this the filter will screw onto a spigot extending from the pump unit and clamp a rubber seal around the hole between the filter and pump.

The pump unit 7 pumps filtered air to face piece 11 via hose 12. The air in the face piece 11 is at a higher pressure than the air within the rest of the suit, however it does not automatically vent into the suit because the exhaust valve 13 is balanced by the pressure in hose 12. During exhalation the pressure inside the face piece rises to cause the exhaust valve to open and vent into the suit. Exhaled air is vented into the suit together with incoming air from hose 12 when exhaust valve 13 opens, and provides ventilating air for the micro-environment within the suit. The ventilating air within the suit 2 is of a higher pressure than the ambient air pressure, and a second exhaust valve 14 vents this air to atmosphere when the pressure differential is sufficient. Pressure sensors may be mounted in the suit to provide control signals to the pump unit and various valves in order to maintain these pressure differentials.

The pump unit operates to respond to breathing demand and increase flow to the face piece when breathing demand increases, such as during strenuous exercise. This produces a corresponding increase in ventilation to the suit. The pump unit operates at a low pressure but will deliver up to in excess of 500 litres of filtered air to the face piece per minute.

Referring now to Figure 2, in this configuration the ventilation to the suit is increased by ventilation being provided directly into the suit via ventilation port 20.

Referring to Figure 3, the ventilation is channelled from port 20, via conduits 31 and 32 to the extremities of the arms and legs respectively.

In Figure 4, the ventilation is channelled via conduit 41 to demist the transparent panel 5. Of course, any and all combinations of these ventilation configurations are possible.

In Figure 5, which is otherwise similar to Figure 2, the exhaled air is passed through balance exhalation valve 50 and ducted directly out of the suit along conduit 51, and not used for ventilation.

Figure 6a shows the flow of air along hose 12 resulting from breathing demand. Air is only drawn during inhalation. In contrast, Figure 6b shows the flow of air along the hose to ventilate the suit. Air flows for this purpose during exhalation, since it flows directly out of exhaust valve 13. The flow for ventilation fall during inhalation as some air is diverted into the lungs.

Figure 6c shows the total flow which can be seen to ripple up during inhalation.

Although the invention has been described with reference to a particular example it should be understood that it could be exemplified in many other ways. For instance, different styles of protective suits may be used, and the ventilating air may come from a different source than the filtered breathing air. Additional filters may be provided at the exhaust ports to filter the breathing and ventilating air as it leaves the suit; this might be useful when the suit is to be worn in sterile environments such as clean rooms.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.