CA1199532A - Materials for thermal protection by rapid smoke production - Google Patents

Abstract

The invention disclosed relates to a device for protection from the heat flash of atomic weapons and comprises a heat-resistant net material, such as nylon, coated with a mixture of neoprene and an explosive initiator. The net material may be formed into clothing for protection of personnel.

Description

~99532 q~his invention relates to a device ~`or protection ~rom the heat flash of atomic weapons. It is intended particularly for the protection of personnel.
Since atomic weapons are quickly becoming an integral part of modern arsenals, considerable a-ttention ls being directed -to the problem o~ protection from the heat flash of these weapons. me nature of the thermal hazard varies greatly with the yield of the weapon. Atomic weapons vary in size from a fraction of a kiloton to as much as 50 to 100 megatons. For the small weapons of less than 1 kiloton the thermal hazard ~one is inside the lethal zone for ionizing radiations, so that at present thermal protection is of little importance. For the larger weapons, protection from thermal flash becomes increasingly importan-t, but also the total tlme over which the the~al radiation energy ls delivered becomes long enough for various simple methods of defence to be applied, e.g. taklng cover.
Some weapons, bowever, present a thermal hazard over times too short for any conscious action to be of use, so that some type o~` constant protection is necessary. For personnel, particularly combat personnel, the usual aim has been to try -to improve considerably the re~ractory ~ualties o~ clothing so that it can withstand the thermal radiation, with-out changing its normal wearing characteristics.
Test work has already been done in the United States on smoking paints for protecting property against thermal radiation. The smoking was initiated by the use of an explosive initiator which was incorporated into the paint. ~ne explosive initiator e.g. tetracene, reacted ins-tant-aneously on being sub~ected to thermal radiation so as to initiate an almost instant production of smoke which in turn absorbed or dispersed the heat. The increase in protection achieved by this system was only marginal.
3 It was the purpose o~ the present development to produce a pl~

1~99532 similar type of coating material for clothing. Inltial tests were directed to determining what were -the most effective initiators and fuels for tlle production ~ smoke. For this type of protection -to be effective the smoke must be produced and -formed into a screen in front of the article to be protected within less than 0.1 seconds of the arrival of the beginning of the heat flash. The heat energy incident during this 0.1 second must raise the surface layers of the targe-t to a high temperature, produce and eject a smoke of adequate density. It was found that the initiators which had been previously used for this purpose in the United States, i.e. con~on explosive initiators, were the most ef~ective, the preferred ones being tetracene, lead styphnate and silver fulminate.
Teats were also conducted to obtain a satisfactory fuel. me function of the fuel is to provide a dense srnoke when vaporised or burnt by the initiator. Numerous fuels were tested, such as anthracene, butyl cement, carbon, starch, sugar, ferrocene and neoprenes, most of which did ~roduce dense smoke but by far the most effective one was found to be a neoprene cement. The compounded neoprene cements were surprisingly effec-tive in producing a u~iform, dense cloud of smoke which effectively absorbed or dispersed the heat. In view of these results the subsequent tests were conducted with neoprene cements as the fuel and tetracene as the initiator.
~hen an efficient combination of initiator and fuel had been determined, attention was directed to the problem of applying this material to clothing. As has been stated above, the main problem with protection of clothing is that the protective material which is added shou~ld intere-fere as little as possible with the nol~al functions of the clothing.
With this in mind, the first experiments were conducted using co~me cial clothing fabrics embossed with small raised dots of the smoke producing mixture. Theintention here was to avoid stiffening the fabric, to retain moisture vapour permeability by leaving a high percentage area unaffected pk - 2 -119~53Z

and to improve~ if possible, the abraslon properties. Ihese features were thought -to be particularly important for protec-ting personnel since a complete covering of the mixture would not only be uncomfortable to wear because it would stiffen the material, but would cause unacceptable heat stress, particularly at high work rates or under tropical conditions.
A number of fabrics prepared in the above manner were exposed in a solar furnace and a considerable amount of protection was obtained. FOL example, a 5 oz. cotton fabric wh,ch would normally char to destruction at an intensity of 5 calories per sq.cm. delivered in 1 second remained undamaged at 6 calories per sq.cm. in 1 second when embossed. ~Iowever~ at higher energies the heat from the burning fuel and emitted vapors damaged the fabric between the dots so that even though the fabric under the dots was undamaged the ma-terial between them was seriously weakened.
Since t~e fabric under the raised dots was protected while the f`abric between the dots was destroyed, it was decided to try to produce a separate protection garment which could be worn over regular clo-tbing so that the protective material would be spaced from -the fabric. ~he pro-tective material would re~uire some form of support, and as stated above, would necessarily have openings to permit air circulation. ~ith this in mind a series of tests were conducted in a solar furnace with fabric nets coated with a mixture of neoprene and tetacene. These -tests showed that such a coated net was extremely effective in protecting fabrics from destruction by thermal radiation and that by the proper selection of mesh size good ventilation could be obtained without damage of the fabric directly behind the opening in the net. m is also permitted the use of a material for the ne-t which was much less f`lamable than ordinary gar-ment material.
Accordingly, the invention in its broadest aspect can be described as beiug a device for protection from thermal radiation which comprises a net coated with a mix-ture of neoprene, pref`erable a compounded neoprene pk - 3 -~9953;~:

cement, and an explosive lnit:iator. To insure good protectlon the ne-t should be made from a heat resis-tant material and nylon has been :~ound to be highly satisfactory for this purpose. Other materials have been tes-ted and have also been found -to be satisfactory. The hole size of the coated net should preferably not be larger than 5 mm. to insure complete protection against radiation intensities up to 30 cal/cm2. in a few seconds.
To produce the coated net of -the invention a nylon ne-t is pre-ferably ~irst co~pletely coated with a compounded neoprene cement. ~his makes an ideal backing since it is totally compatible with the neoprene-tetracene mixture and has the additional qualities of being quite resistant to both heat and wear. One or more coatings of a neoprene-tetracene mixture are then applied to one surface o~' the neoprene-coated net. T~le neoprene-tetracene mixture should contain at least ~ by wei~ht of tet-racene and preferably about 8~ based on the solid content.
The attached drawing is a schematic illus-tration of the rel-ative positions of the incidenb thermal radiation~ the protective net and the object protected. As can be seen from the drawing, the surface of the net facing ~he incident radiation is coat.ed with the neoprene-initiator mixture and the smoke is emitted in the direction of the incident; radiation.
The actual amount of neoprene-tetracene mixture to be applied to the net can vary greatly. I-t has been found that the rate of emission of smoke is dependent on the intensity of the radiation so that the actual thickness of the coating will be dependent on the anticipated in-tensity of radiation and the length of time which the coating is expected to be subjected to the radiation. For protection of inanima-te objects which~annot take avoiding action it is probable that thicker coatings would be needed than for protection of personnel.
The sequence of events which occur during the smoke production is that first a small amount of the radiant energy i6 reflected without any resultant thermal stress, and since -the neoprene-tetracene mixture is pk - 4 -l~9S3~

nearly black, being ~rom 0.3 to 2.5 microns, this reflection is often only a very ~ew percent. Next all o~ the remaining radiant energy is absorbed while penetrating a very small distance beneath the surface of the mixt~re. The resultant temperature rise explodes the initiator and burns the ~uel. ~hese reactions are exothermic and material is ejected and forms a smoke which scatters and absorbs the incoming rad-iant energy. During and following this period energy is transferred in all directions (but mostly in the direction opposite to that of the incident radiation) by mass transfer o~ gases, vapors or small pieces of material. Some mass trans*er can, o~ course, occur back through the holes of the net but this is a relatively minor amount. The heat developed in the material o~ the net is conducted to the near surface and then trans~erred by conduction through the air to the target. A small amount o~ heat may be re-radiated at long wave lengths khrough the net holes or from the surface of the net ~aclng the ~abric being protected.

To test the protective nets of this inventlon a series o~
coating compounds were prepared as follo~s:
Compound No. 1 Neoprene 100.00 Zinc Oxide 10.00 Magnesia 10.00 "Nonox WSP"l 2.00 "Calcene qM~-250.00 "Xi Sil 233"~20.00 Titanium Dioxide 10.00

2-Mercaptoimidazoline 0.50 1 "Nonox WSP" is the trade mark of Imperial Chemical Industires ~or an alkylated bis-phenol.
2 "Calcene TM" is tne trade mark of Columbia-Southern Chemical Corp.
for fine particle, precipitated calcium carbonate pigmen-t.

3 "Hi Sil 233" is the trade mark o~ Columbia-Southern Chemical Corp -~or hydrated silica js -5-Compound No 2 Compound l 202.50 "Chlorowax 70--1 10.00 Antimony Irioxide 40.00 1 "Chlorowax 70" is the trade mark of Diamond Alkali Co. for a chlorin-ated paraffin wax.
Compound No. 3 Neoprene lO0.00 Zinc Oxide 10.00 Magnesia 10.00 Symmetrical di-beta-napht~yl-para-phenyl-ene diamine 2.00 Phenyl-E-naphthyl-amine 2.00 2-Mercaptoimidazoline 0.50 Compound No. 4 Compound 3 124.50 EPC Black 25.00 Compound No. 5 Compouna 3 121~.50 "Mineralite 3X"l50.00 "Chlorowax 70" lO.00 Antimony Trioxide 40.00 1 "Mineralite 3X" is the trade mark of Mineralite Sales Corp. for a mica-type filler.
lhese compounds were then used for prep~rine coating solutions.
To coat the nets they were dipped ~n a x~lene solution of one of the above compounds and cured by heating. The nets were dipped several times in the solution, the number of dips being determined by the thickness of coating desired. The ~inal coating layer was produced from a xylene solution of one of the above compounds to which was added 8 parts of tetracene per lO0 parts of solids.

js -6-.~

TABIE :[
Details of the smoke-producing ne-ts used in Examples 1 - 13 . ........... _ . . ~ l Final Net Base Ne Base Base Coa-t Layer 1 Layer 2 Final Sq. Yd.
No . Type Coat Cure ~ Cure Wt .
. .. _............ _ _ PNl Type A No. 1 30 mins No . 4 No. 4 T No . 4 17 - 9 15% solids at 250F. 209b solid ¦ Tetracene Dips - ~ 20~ solids PN2 Type B No. 1 30 mins. No. 4 No.4 +
15~o solids at 250F 20~ solids Tetracene _ _ 20.2 Dips - 4 20% Solids .
PN3 Type B No. 2 30 mins. No.l~(a) No.4(a) ~
15~b solids at 250F. 15~h solids Te-tracene __ 18.5 Dips - 4 15~ solids .. _ _ _ PN4 Type B No .2 30 mins . No .4 ( a ) +
157b solids at 250F Te-tracene __ __ 11.9 15~ Solids _. _ PN5 Type B No.5 60 mins . No.4(a )-~ 60 mins .
Coloured at 280F. Tetracene __ at 200 ¦ 12.0 Olive Drab 15~ Solids 20~o solids ~ ~ _ PN6 Type B No.5 60 mins. No.3(a) 60 mins.
Coloured At 280F. Coloured ___ at 200F 11.]
Olive Drab Olive Drab 20% SoIids + Tetracene ~ 15~ Solids PN7 Type B No .5 60 mins . No .4 ( a ) +
Coloured at 280F. Tetracene ___ 60 mins.
Olive Drab 15~o Solids at 200F 13.5 20~ Solids i _ The desi~ation (a) a~ter the compound ~wnber indicates that an acceler-ator was added to the solution in an amount o~ 8 parts per 100 parts solids.

pk - 7 -~1~9953~

Two types of nylon net were used and these will be designated hereinaEter as Type A and rrype B.
Type A is a 100~ nylon net of 4 oz/yd2 with a hole si~e o-~approximately 4 mm, about 6 holes per inch in warp direction and 4 holes per inch in weft direction.
Type B is 100~ nylon, 5 oz/sq.yd., hole si~e 2 mms., 6 holes warpways and 10 holes we~tways.
Details of a series of nets which were coated in t~le above malmer are described in Table I and these nets were used as the protective nets in -the following tests.
Example I
A sample of 13 oz./yd2 Khaki coloured all wool battle dress serge was subJect without any protection to an exposure intensity of 8 cal/
cm2 in 1 second in a solar furnace. After the exposure the fabric was visibly charred and it had no appreciable bursting strength.
Example 2 Example I was repeated at an exposure intensity of 20 cal/cm2 with protective net PN 1 as described in Table I in front of and in contac-t with the ~abric. h~en though the intensity of the radiation was 2 1/2 times the intensity in Example I, the fabric was only very slightly singed and the bursting strength was reduced by only about 10~.
Example 3 Example 2 was repeated at an exposure intensity of 30 cal/cm2 and in this case the fabric was singedin the pattern of the net and the bursting strength was reduced by about 25~.
Example 4 Example 3 was next repeated using a different protective net, the net in this case being PN 2 which had a mesh opening O:L 2 mm.
notable improvement was obtained over Example 3 since the fabric ~ascnly very slightly singed and the bursting strength remained unchanged.

pk 1~953Z

Ex le 5 Example 4 was repea-ted with protective net PN3. This was the same baslc nylon net as PN2 but the coa-ting contained an accelerator and was slightly lighter than PN2. lhe results with PN3 were the same as with PN2~
Example 6 Example I was repeated with 9 oz./yd2 navy blue RCN cotton drill in place of the battle dress. As with the battle dress, -the fabric was severely charred~
Example 7 A sample of 9 oz./yd2 navy blue RCN cotton drill ~as sub~ected to an exposure intensity of 30 cal./cm2 while being protected by protection net PN5 place 5 mm in front of the fabric. P~5 is a relati~ely light wei~ht protective net. After an exposure of 1 sec. the fabric was only slightly discoloured and the bursting strength was unchanged.
Example 8 Example 7 was repeated at an exposure intensity o~ 20 cal/cm2 with the protective net Ln contact with the fabric. Again the fabric was only discoloured but the bursting strength was reduced by 75~.
Example 9 E.xsmple ~ was repeated substituting a Canadian Army Summer dress fabric which was a 5 oz./yd2 mixed nylon and cotton fabric~ for the RCN
drill. After exposure the fabric was slightly singed and tke bursting s-trength was reduced by about 2/3.
Example l_ A protective net P~ 3, which was heavier than PN 5, was placed in contact with a o.3 oz.lyd2 nylon/cctton combat cloth and subJected to thermal radiation in a solar furnace. The intensity was 30 cal/cm2 and a~ter a 1 sec. exposure the fabric was slightly singed and -the burs-ting strength was reduced by 25~.

pk _ g _ ~99S32 ~ e~ts we.re also conducted to dete~ine the e~fectiveness of the protective nets as well as the nets toge~her with the above fabrics in protecting bare flesh. These tests were conducted by placing a pro-tective net or net and piece uf fabric over the bare skin of' the inner forearm and subjecting this to thermal radiation. Such tests are relevant -to the problem o~ protecting norrmally unclothed areas such as the eye areas and the hands, for which cases the net is considered suitable Example 11 1 layer o~ protective net PN 1 was spaced 5 mm from the bare skin o~ the inner forearm and this was subjected to exposures o~ varying intensities in a solar furnace. After 1 sec. exposure at 10 cal/cm2 and 15 cal./cm2 t,he skin was slightly reddened. A~, a 20 cal/cm intensity, at`ter 1 sec the skin was discoloured and several days af`ter the exposure sli~rt blis-tering was no-ted.
~ ple 12 A layer o* pro-tec-tive net PN 1 and a layer o~ battledress serge or RCN cotton drill were placed in contact with the bare skin of àn inner forearm and subjected to a radiation intensity of 30 cal/cm2 in a solar furnace. me exposure was for 1 second and no immediate effcct was noted wit.h either combination. However, i~ the heated cloth was held in contact ~i-th the skin for some time sli~ht erythema occured.
xample 13 ~ layer of protective net PN 1 and a layer of cotton-nylon combat cloth were placed on the bare skin of an inner forearm. This was subjected to an exposure intensity of 15 cal/cm2 for 1 second and no effect on the skin could be noted.
mese experiments have shown tha-t the coa-ted net is extremely effective in protecting against thermal radiation and that very little radian-t energy penetrates the holes of the nets used. m is would cl.early indicate that most of the energy is absorbed or scattered by the smoke 1~99~ 2 Although it is realized that a net worn over clothing might have certain disadvantages these are heavily out-weighted by its many desirable properties. As we have stated above, the coated net is very durable under intense radiation and while the smoke absorbs and scatters the heat waves so that they do not pass between the open spaces in the net, these spaces ser~e an essential purpose in tha-t they provide ventilation for the person being protected with -the result that heat stress due to a water-vapour impermeable layer is avoided. This is very important in clothing. Also it has been found by ~ield tests that clothing made from the nets of this invention does not have any more tendency to snag than orthodox clothing, nor do the nets cause di~ziness when used for several hours to protect the eye areas.
The above discussion has been directed excluslvely to the pro-tection of personnel, but it-will be appreciated that the protective device of this invention has a much wider applicability. For exampie, buildings, vehicles, etc. all represent quite good forms of protection against thermal radiation but most of these have one maJor hazard which is the entry of radiation t.hrough windows. The coated net of this invention could be useful as screens over windows to prevent such entry of radia-tion.
Another usefor these nets would be for the protection of ammunition and equipment which is stored in the open. Particularly when used for protecting buildings and materials, in which case a thick coating of the neoprene-tetracene mixture can be used, the protective material has the advan-tage that the emission o~ smoke ceases instantaneously with the termination of the thermal radiation and will commence again on being again subjected to radiation. This can be repeated until the fuel supply for the smoke has been exhausted. The nets tend to be self extinguishlng after exposure to radiant energy, and are less likely to catch fire than normal clothing fabrics.
3o pk - 11 -

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE AS CLAIMED ARE DEFINED AS FOLLOWS:

1. A device for protection from thermal radiation which comprises a net coated with a mixture of neoprene and an explosive initiator.

2. A device for protection from thermal radiation which comprises a net coated with a mixture of neoprene and at least one explosive initiator selected from the group consisting of tetracene, lead styphnate and silver fulminate

3. A device as claimed in claim 2 wherein the net has a base coating of neoprene containing no tetracene.

4. A device as claimed in claim 1, 2 or 3 wherein the neoprene is in the form of a compounded neoprene cement.

5. A device as claimed in claim 1, 2 or 3 wherein the net is nylon.

6. A device as claimed in claim 1, 2 or 3 wherein the coating is applied to only one face of the net.

7. A device for protection from thermal radiation which comprises a nylon net coated on one face with a mixture of a compounded neoprene cement and tetracene.

8. A device for protection from thermal radiation which comprises a nylon net completely coated with a compounded neoprene cement and fur-ther coated on one face with an external layer of a mixture of compounded neoprene cement and tetracene.

9. A device as claimed in claim 8 wherein the concentration of the tetracene in the mixture is approximately 8% by weight, calculated on the solids content of the compounded cement.