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Smoke grenades are canister-
type grenades used as
ground-to-ground or ground-to-air signalling devices, target or
landing zone marking devices, or a screening devices for unit
movements. Smoke grenades are normally considered non lethal,
although incorrect use may cause injury or fatality. The body
consists of a sheet steel cylinder with a few emission holes on
top
and at the bottom to allow smoke release when the grenade is
ignited. The filler consists of 250 to 350 grams of coloured (red,
green, orange, gray, yellow, blue, white, black, or violet) smoke
mixture (mostly potassium chlorate, lactose and a dye).
The reaction is exothermic and
grenade casings will remain scalding hot for some time even after the grenade
is
no longer emitting smoke. |
| Smoke
grenade |
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Another type of smoke
grenades are the bursting kind. These are
filled with white phosphorus (WP), which is spread by explosive
action. White phosphorus catches fire in the presence of air, and
burns with a brilliant yellow flame, while producing copious
amounts
of white smoke (phosphorus pentoxide). These double as incendiary
grenades (q.v.), and a variant of these are also launched from
infantry-portable or armoured fighting vehicle-mounted grenade
launchers. Users must also be wary of wind direction when using
smoke grenades.
Smoke grenades should not be confused with smoke bombs, which are
typically started with an external fuse rather than a pin.
Artillery and mortars can also fire smoke generating
munitions, and are the main means of
generating tactical smokescreens on land. As with grenades, artillery shells
are available as both emission type smoke shell, and bursting
smoke shell. Mortars nearly always use bursting smoke rounds because of the
smaller size of mortar bombs and the greater efficiency of bursting rounds.
Very large or sustained smoke screens are produced by a
smoke generator. This is a machine which heats a volatile material (typically
oil or an oil based mixture) to evaporate it, then mixes the vapour with cool
external air at a controlled rate so it condenses to a mist
with a controlled droplet size. Cruder designs simply boiled waste oil over a
heater, while more sophisticated ones sprayed a specially
formulated oily composition ("fog oil") through nozzles onto a heated plate.
Choice of a suitable oil, and careful control of cooling rate,
can produce droplet sizes close to the ideal size for Mie scattering of
visible light.
This produces a very effective obscuration per weight of material used. This
screen can then be sustained as long as the generator is supplied
with oil, and—especially if a number of generators are used—the screen can
build up to a considerable size. One 50 gallon drum of fog oil can
obscure 60 miles of land in 15 minutes.
Whilst producing very large amounts of smoke relatively
cheaply, these generators have a number of disadvantages. They are much slower
to respond than pyrotechnic sources, and require a valuable piece of equipment
to be sited at the point of emission of the smoke. They are
also relatively heavy and not readily portable, which is a significant problem
if the wind shifts. To overcome this latter problem they may be
used in fixed posts widely dispersed over the battlefield, or else mounted on
specially adapted vehicles. An example of the latter is the M56 Coyote
generator.
Warships have sometimes used a simple variation of the
smoke generator, by injecting fuel oil directly into the smoke stack. They
also use large floating smoke canisters, known as smoke buoys. In the past
they have also used sprays of chemicals that fume on contact with
air, such as titanium tetrachloride.
The proliferation of thermal imaging FLIR systems on the
battlefields necessitates the use of obscurant smokes that are effectively
opaque in the infrared
part of electromagnetic spectrum. To achieve this, the particle size and
composition of the smokes has to be adjusted. One of the approaches
is using an aerosol of burning red phosphorus particles and aluminium coated
glass
fibres; the infrared emissions of such smoke curtains
hides the weaker emissions of colder objects behind it, but the effect is only
short-lived. Carbon (most often graphite) particles present in the smokes can
also serve to absorb the beams of laser designators. Yet another possibility
is a water fog
sprayed around the vehicle; the presence of large droplets absorbs in infrared
band and additionally serves as a countermeasure against radars in 94 GHz
band. Other materials used as visible/infrared obscurants are micropulverized
flakes of brass or graphite,
particles of titanium dioxide, or terephthalic acid.
Older systems for production of infrared smoke work as generators of aerosol
of dust with controlled particle size. Most contemporary vehicle-mounted
systems use this approach. However the aerosol stays airborne only for a short
time.
The brass particles used in some infrared smoke grenades are typically
composed of 70% copper and 30% zinc.
They are shaped as irregular flakes with a diameter of about 1.7 µm and
thickness of 80-320 nm.
A reportedly good improvised system for production of aerosol effective even
in far infrared is said to be a dry powder fire extinguisher.
Some experimental obscurants work in both infrared and millimetre wave region.
They include carbon
fibres, metal coated fibres or glass particles,
metal microwires, particles of iron and of suitable polymers.
Zinc chloride smoke is grey-white and consists of tiny
particles of zinc chloride. The most common mixture for generating these is
the zinc chloride smoke mixture (HC), consisting of
hexachloroethane, grained aluminium and zinc oxide. The smoke consists of zinc
chloride, zinc oxychlorides, and hydrochloric acid, which absorb the moisture
in the air. The smoke also contains traces of organic chlorinated compounds,
phosgene, carbon monoxide, and chlorine.
Its toxicity is caused mainly by the content of strongly
acidic
hydrochloric acid, but also due to thermal effects of reaction of zinc
chloride with water. These effects cause lesions of the mucous membranes
of the upper airways. Damage of the lower airways can manifest itself later as
well, due to fine particles of zinc chloride and traces of
phosgene. In high concentrations the smoke can be very dangerous when
inhaled. Symptoms include dyspnea, retrosternal pain, hoarseness, stridor,
lachrymation, cough, expectoration, and in some cases haemoptysis.
Delayed pulmonary edema, cyanosis or bronchopneumonia may develop. The smoke
and the spent canisters contain suspected carcinogens.
The prognosis for the casualties depends on the degree of the pulmonary
damage. All exposed individuals should be kept under
observation for 8 hours. Most affected individuals recover within several
days, with some symptoms persisting for up to 1-2 weeks. Severe
cases can suffer of reduced pulmonary function for some months, the worst
cases developing marked dyspnea and cyanosis leading to death.
Respirators are required for people coming into contact with the zinc chloride
smoke.
Chlorosulfuric acid (CSA) is a heavy, strongly
acidic liquid. When dispensed in air, it readily absorbs moisture and forms
dense white fog of hydrochloric acid and
sulphuric acid. In moderate concentrations it is highly irritating to eyes,
nose, and skin.
When chlorosulfuric acid comes in contact with water, a
strong exothermic reaction scatters the corrosive mixture in all directions.
CSA is highly corrosive, so careful handling is required.
Low concentrations cause prickling sensations on the skin, but high
concentrations or prolonged exposure to field concentrations can cause
severe irritation of the eyes, skin, and respiratory tract, and mild cough and
moderate contact dermatitis can result. Liquid CSA causes acid burns of skin
and exposure of eyes can lead to severe eye damage.
Affected body parts should be washed with water and then with sodium
bicarbonate solution. The burns are then treated like thermal burns. The skin
burns
heal readily, while cornea burns can result in residual scarring.
Respirators are required for any concentrations sufficient to cause any
coughing, irritation of the eyes or prickling of the skin.
Titanium tetrachloride (FM) is a yellow, non-
flammable, corrosive liquid. In contact with damp air
it hydrolyzes readily, resulting in a dense white smoke consisting of droplets
of hydrochloric acid and particles of titanium oxychloride.
The titanium tetrachloride smoke is irritant and unpleasant to breathe.
It is dispensed from aircraft to create vertical smoke curtains, and during
World War II it was a
favourite smoke generation agent on
warships.
Goggles or a respirator should be worn when in contact with the smoke, full
protective clothing should be worn when handling liquid FM.
In direct contact with skin or eyes, liquid FM causes acid burns.
Red phosphorus and white phosphorus (WP) are red or
waxy yellow or white substances. White phosphorus is pyrophoric - can be
handled safely when under water, but in contact with air it spontaneously
ignites. It is used as an incendiary. Both types of phosphorus are used for
smoke generation, mostly in artillery shells, bombs, and grenades.
White phosphorus smoke is typically very hot and may cause
burns on contact. Red phosphorus is less reactive, does not ignite
spontaneously, and its smoke does not cause thermal burns - for this reason it
is safer to handle, but cannot be used so easily as an
incendiary.
Aerosol of burning phosphorus articles is an effective obscurant against
thermal imaging systems. However, this effect is only very short-lived, and
after the
phosphorus particles are fully burned, the smoke reverts from emission to
absorption. While very effective in visible spectrum, cool
phosphorus smoke has only low absorption and scattering in infrared
wavelengths. Additives can be present in the smoke which cover this
part of the spectrum.
Oil smoke is usually produced by smoke generators. The
resulting "smoke" is a mist of oil droplets of controlled size, and
is therefore technically not smoke but fog. Rather than being produced by the
combustion of fog oil, it is produced by heating of fog oil, the
release of hot (but not burnt) fog oil into the air, and the condensing of hot
fog oil on contact with air.
Particles of graphite can be added to oil mist to make it opaque in infrared
spectrum, providing additional degree of protection against thermal imaging
and laser designators.
Various signalling purposes require the use of coloured
smoke. The smoke created is a fine mist of dye particles,
generated by burning a mixture of one or more dyes with a low-temperature
pyrotechnic composition, usually based on potassium chlorate and lactose (also
known as milk sugar).
Coloured smoke screen is also possible by adding a coloured
dye into the fog oil mixture. Typical white smoke screen uses titanium dioxide
(or other white pigment), but other colours are possible by replacing titanium
dioxide with another pigment. When the hot fog oil condenses
on contact with air, the pigment particles are suspended along with the oil
vapour. Early smoke screen experiments attempted the use of coloured
pigment, but found that titanium dioxide was the most light scattering
particle known and therefore best for use in obscuring troops and naval
vessels. Coloured smoke became primarily used for signalling rather than
obscuring. In today's military, smoke grenades are found to be
non-cancer causing, unlike the 50's AN-M8 model.
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Smoke screens are usually used by infantry to conceal their
movement
in areas of exposure to enemy fire. They can also be used by armoured fighting
vehicles, such as tanks, to conceal a withdrawal.
For the crossing of the Dnieper river in October 1943, the Red Army laid a
smoke screen 30 kilometres (18 miles) long. At the Anzio beachhead in 1944,
US Chemical Corps troops maintained a 25 km (15 mile) "light haze" smokescreen
around the harbour throughout daylight hours, for two
months. The density of this screen was adjusted to be sufficient to prevent
observation by German forward observers in the surrounding
hills, yet not inhibit port operations.
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| A smoke
grenade being used during a military training exercise |
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There are a number of early examples of using incendiary
weapons at sea, such as Greek fire, stinkpots, fire ships, and incendiaries on
the decks of turtle ships, which also had the effect of creating smoke. The
naval smoke screen is often said to have been proposed by Sir Thomas Cochrane
in 1812,
although Sir Cochrane's proposal was as much an asphyxiant as an obscurant. It
is not until the early twentieth century that we get
clear evidence of deliberate use of large scale naval smokescreens as a major
tactic.
Smoke screens were used during the Battle of Jutland in World War I.
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In the Battle of the River Plate in World War II, the
German pocket battleship Admiral Graf Spee used a smoke screen to
escape from the British cruisers.
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In the Second Battle of the Atlantic in World War II, smoke
screens were used by Allied destroyer escorts to mask the presence of the
merchant ships from German U-boats.
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At the Battle off Samar in October 1944, Taffy Three, the
American Escort Carrier task unit,
the escorts laid a smoke screen to allow the carriers to escape, and add to
the general confusion.
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