PROTECTIVE CLOTHING

Abstract: An article of protective clothing designed for protection against blast has a first sheet (11) of solid material backed by a second sheet (12) of pneumatic material, the physical properties and dimensions of the two sheets (11, 12) being such that an acoustic decoupling effect is provided which greatly reduces the pressure wave effect on the body of a person wearing the clothing. The first sheet (11) might by of GRP, 9 mm thick with an areal density of 20 kg/square metre and a second sheet (12) of pneumatic material having a nominal thickness of 20 mm, 94 % air content and a density of 45 kg/cubic metre.

Description: PROTECTIVE CLOTHING The present invention relates to protective clothing. Many types of protective clothing, for use in environments where a wearer may be exposed to fragments or bullets are know. Efforts have been made to improve the performance of such armour against the effects of air blast (shock, or pressure, waves). However, no protective clothing has yet been developed which is truly effective against shock waves in air. The effect of blast (which is the direct impact of a shock wave) on a person's body has two effects, namely gross deformation of the body and the transmission of a high velocity stress wave through the body tissue. It has, in the past, been thought that the lung and bowel injury resulting from the shock wave was caused by deformation of the body, and the design of protective clothing has been based on this premise. It has now been discovered that, in fact, the main damage is caused by the direct coupling of shock waves into the body. This explains the fact that neither solid nor resilient protective clothing have been able to provide the expected protection. Solid clothing contacting a body allows direct transmission of pressure waves, and resilient material, such as foam, may well give an acoustic coupling effect which, as has been discovered, increased the internal injury. According to the present invention an article of protective clothing includes at least two contacting sheets of material, characterised in having a first, outer, sheet formed of solid material having an areal density of 18 to 22 kg/square metre and a thickness of 8 to 10 mm; and a second, inner, sheet formed of a pneumatic material having a density of 40-50 kg/cubic metre, an air content of 92 to 96% and a thickness of 17 to 23 mm. The Applicant has found that an article of protective clothing containing this feature, and of a nature no more cumbersome, or heavy, than conventional protective clothing can provide an acoustic decoupling effect which greatly reduces the pressure wave effect on the body of a person wearing the clothing. Many articles of protective clothing having an outer sheet of solid material and an inner sheet of pneumatic material, usually in combination with further sheets of material, have been described in the prior art. For example US 3,559,210 a d 3,873,998 describe protective clothing intended for protection against missiles such as bullets in which a sheet of solid material has secondary sheets in front and behind, these secondary sheets being designed to prevent injury caused by spall - this is small fragments caused by disintegration of missile and solid sheet material upon impact. These items of protective clothing contain sheets of pneumatic material which is intended to reduce the transmission of impact effects to a wearer's body, to improve comfort, or both. Similar articles of protective clothing, also intended for protection against missiles are described in UK Patent 915,345; 1,106,175 and 1,556,245 and in UK Patent Application 2,210,773A. All the prior art documents are concerned with protection against missiles and none mention the effects of blast. Where physical properties and dimensions are mentioned these do not impinge on those required by the present invention. These prior art articles might be expected to give only limited protection against blast, and, in some cases, as explained above, might actually increase blast effects. In one form of the invention the first sheet is formed from 9 mm thick Glass Reinforced Plastic (GRP) having an areal density of 20 kg/sq metre, and the second sheet is formed from a sheet of material having a nominal thickness of 20mm and an air content of 94% and a Density of 45kg/square metre. Alternative materials, such as a ceramic, a metal such as steel or some other form of Fibre Reinforced Plastic (FRP) material might be used, in which case the physical properties and dimensions may need to be varied slightly for maximum effect. In an improved form of the invention a third sheet of solid material having a thickness of between 0.40 and 0.44 mm and an areal density of 4.5 to 4.9 kg/square metre divides the second sheet into two sub-sheets, the sub-sheets being preferably of roughly equal thickness and having a combined thickness in the order of 17 to 23 mm. The third sheet might be of, for example, lead, steel or lead filled plastic. In one form of the invention the third sheet is lead, is 0.42 mm thick and has an areal density of 4.7 kg/square metre. The pneumatic material might be, for example, Plastazote (RTM). Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is a perspective view of an article of protective clothing, Figure 2 is an elevation, in section along line 1-1 of Figure 1 of one embodiment of the invention, Figure 3 is an elevation, in section along line 1-1 of Figure 1 of another embodiment of the invention, Figure 4 is a graph of the decoupling effects of the embodiments of Figures 2 and 3, and Figure 5 is a Bar Chart showing effects of blast with various protection. An article of protective clothing shown generally at 10 in Figure 1 consists (Figure 2) of a first sheet 11 of GRP material, 9 mm thick and having an areal density of 20 kg/square metre, which is in contact with a second sheet 12 of pneumatic material, such as Plastazote (RTM), having a nominal thickness of 20mm and an air content of 94% and a density of 45 kg/cubic metre. In an alternative form of the invention (Figure 3) (0.42 mm thick and having an areal density of 4.7 kg/cubic metre) a third sheet 13 of lead divides the second sheet into two sub-sheets 14,15. Alternative materials for the various layers are, of course, possible. For example steel or another metal, or some FRP material other than GRP, may be used for the first sheet 11, and iron or lead filled plastic for the third sheet 13. The physical properties and dimensions for best effect will then vary slightly compared with those quoted above. Those skilled in the art will be aware that acousting decoupling effects are frequency responsive, and that care must be taken in designing the clothing to ensure that decoupling rather than coupling occurs. The Applicant has found that, in general, the thickness of the first and second sheets to give satisfactory results lie within the range of thicknesses commonly used in conventional clothing of this type. The two embodiments of the invention illustrated in Figures 2 and 3 were tested for their decoupling effect in transmitting shock waves from air to water over a frequency band of 0-6.25 kHZ. The results are shown in Figure 4, from which it can be seen that the layer version gives improved decoupling at the frequencies, greater than 1.5 kHz, considered to result in lung and bowel injuries. The results translated into their effect in preventing blast damage to a body are shown in Figure 5, where Qi is the "quotient of lung injury", and equals Actual lung weight divided by Predicted normal lung weight, and the blast overpressure to which the results relate was 300-400 kPa incident (1100-1700 kPa reflected). In some embodiments of the invention, more solid sheets might further subdivide the second sheet 12.

Claims: CLAIMS What is claimed is: 1. An article of protective clothing, including at least two contacting sheets (11,12) of material, characterised in that a first, outer sheet (11) is formed of solid material having an areal density of 18 to 22 kg/square metre and a thickness of 8 to 10 mm, and a second, inner, sheet (12) is formed of a pneumatic material having a density of 40-50 kg/cubic metre, an air content of 92-96% and a thickness of 17 to 23 mm. 2. An article as claimed in Claim 1 characterised in that the first sheet (11) is formed of FRP, of metal, or of a ceramic material. 3. An article as claimed in Claim 2 characterised in that the material is GRP. 4. An article as claimed in Claim 3 characterised in that the thickness of the first sheet (11) is 0.9 mm. 5. An article as claimed in Claim 3 or in Claim 4 characterised in that the first sheet (11) has an areal density of 20 kg/square metre. 6. An article as claimed in any one of Claims 1 to 5 characterised in that the second sheet (12) has a density of 45 kg/cubic metre, an air content of 94% and a nominal thickness of 20 mm. 7. An article as claimed in any one of Claims 1 to 6 characterised in that a third sheet (13) divides the second sheet into two sub-sheets (14,15), the third sheet (13) being 0.40 to 0.44 mm thick and having an areal density of 4.5 to 4.9 kg/square metre. 8. An article as claimed in Claim 7 characterised in that the third sheet (13) is formed of iron, steel, lead or lead filled plastic material. 9. An article as claimed in Claim 8 characterised in that the third sheet (13) is of lead. 10. An article as claimed in Claim 9 characterised in that the third sheet (13) is 0.42 mm thick and has an areal density of 4.7 kg/square metre.

Inventors: CATER STEPHEN JOHN, COOPER GRAHAM JOHN, TOWNED DAVID JOHN, CATER, STEPHEN, JOHN, COOPER, GRAHAM, JOHN, TOWNED, DAVID, JOHN
Applicants: SECR DEFENCE BRIT, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNI
Application year: 1991
Main classification: F41H1
IPC codes: A41D31, B32B7, F41H5