Date post: | 10-Apr-2023 |
Category: |
Documents |
Upload: | khangminh22 |
View: | 0 times |
Download: | 0 times |
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
SUBJECT FORENSIC SCIENCE
Paper No. and Title PAPER No.10: Forensic Toxicology
Module No. and Title MODULE No. 18: Poisonous Gases
Module Tag FSC_P10_M18
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
TABLE OF CONTENTS
1. Learning Outcomes
2. Introduction
3. Classification of Poisons Gases
3.1 Simple Asphyxiants
3.2 Respiratory Irritants
3.3 Systemic Asphyxiants
3.4 Volatile Compounds
4. Some Notable Poisonous Gases
4.1. Carbon Monoxide
4.2. Carbon Dioxide
4.3. Methyl Isocyanate
4.4. Hydrogen Sulphide
4.5. Aliphatic Hydrocarbons
4.6. Ammonia
4.7. Phosgene
4.8. Phosphine
4.9. Hydrogen Cyanide
4.10. Chlorine
5. Warfare Gases
6. Forensic Analysis of some Poison Gases
7. Summary
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
1. Learning Outcomes
After studying this module, you shall be able to know about-
The significance of Poisonous Gases
Classification and Forensic importance of Poisonous Gases
Forensic Examination of Poisonous Gases
2. Introduction
Toxicology is the study of poisons, or, more comprehensively, the identification and
quantification of adverse outcomes associated with exposures to physical agents, chemical
substances and other conditions. One of such agents is Gaseous Poisons or Asphyxiants.
Basically an asphyxiant is a substance that can cause unconsciousness or death by
asphyxiation (suffocation). Cases of gaseous poisoning are mostly accidental in nature, but
that does not exclusively means that homicidal use of gaseous poisons are not reported.
Example for the latter use can be the use of Warfare gases which have been discussed in this
module. However, the cases related to poison gases are mostly encountered by the forensic
experts are accidental in nature. Gaseous poisons are very rapidly absorbed and are
consequently produce most rapid effect. While, in the cases of solid or liquid poisons the fatal
dose is signified as Lethal Dose or LD50, the same is indicated as LC50 in case of Gaseous
Poisons. LC50 or Lethal Concentration is the standard measure of the noxiousness of the
surrounding medium that will exterminate half of the sample population of a specific test-
animal in a specified period through exposure by way of inhalation (respiration). LC50 is
measured in micrograms (or milligrams) of the material per litre, or parts per million (ppm),
of air or water. It is important to note that lower the amount, more toxic is the material. LC50
values cannot be directly inferred from one species to the other or to humans.
3. Classification of Poison Gases
Poisonous Gases or Asphyxiants are classified as:
3.1 Simple Asphyxiants
These gases displace oxygen from the ambient air and reduce the partial pressure of available
oxygen. Examples include Carbon Dioxide, Nitrogen, Aliphatic Hydrocarbon gases (Butane,
Ethane, Methane, and Propane), and Noble Gases (Argon, Helium, Neon, Radon, and
Xenon).
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
3.2 Respiratory Irritants
These gases damage the respiratory tract by destroying the integrity of the mucosal barrier.
Examples include Acrolein, Ammonia, Chloramine, Chlorine, Formaldehyde, Hydrogen
Sulphide, Methyl Bromide, Methyl Isocyanate, Oxides of Nitrogen, Osmium Tetroxide,
Ozone, Phosgene, and Sulphur Dioxide. Heavy metal-related gases also come under this
category (e.g., cadmium fumes, copper fumes, mercury vapour, zinc chloride and zinc oxide).
3.3 Systemic Asphyxiants
These are the inert gases and when these gases are breathed in high concentration, they act
mechanically by displacing or excluding oxygen. These gases produce significant systemic
toxicity by specialised mechanisms. Examples include Carbon Monoxide, Cyanide, and
smoke. It must be noted that systemic toxicity may also be observed in the case of some
simple asphyxiants and respiratory irritants, though it is not the principal feature.
3.4 Volatile Compounds
Volatile compounds have little or no irritant effect after absorption; they act as an anaesthetic
agent or toxic to the liver, kidney etc. Examples are: Aliphatic hydrocarbons, Halogenated
hydrocarbons, Aromatic hydrocarbons.
4. Some Notable Poisonous Gases
4.1 Carbon Monoxide (LC50 = 3,760 ppm)
Carbon Monoxide is colourless, tasteless and lighter than air with a garlicky odour. It is a
highly poisonous gas that is absorbed in to the lungs and combines with haemoglobin of the
RBC in the blood and forms a stable compound carboxyhaemoglobin. The affinity of
haemoglobin for Carbon Monoxide has 200-300 times greater for haemoglobin than that of
oxygen. It reduces oxygen content of blood and then of tissues.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
Next to carbon dioxide, carbon Monoxide is the most abundant atmospheric pollutant and is
progressively increasing in concentration. Apart from its role as an environmental
contaminant, Carbon Monoxide is responsible for a significant number of deaths encountered
in forensic practice. Accidental Carbon Monoxide poisoning can occur in several other
situations apart from domestic exposure. Internal combustion engine exhaust fumes,
malfunctioning home heating systems, gas hot water heaters, gas clothes dryers, charcoal and
poorly vented wood/coal stoves, space heaters, gas and kerosene lanterns, and fires in
buildings are common sources of Carbon Monoxide. In Carbon Monoxide poisoning the
colour of the skin is cherry red due to carboxyhaemoglobin; the colour is characteristic of the
poisoning but its absence by no means excludes it.
4.2 Carbon Dioxide (LC50 = 250ppm)
Carbon Dioxide is colourless, odourless, non-flammable gas which is heavier than air. In its
solid form (dry ice) it is whitish in colour and acts as a corrosive. The carbon dioxide
intoxication usually results from the physiological disturbances. The gas may disperse slowly
if ventilation is poor. It is used as Fire extinguisher, in Carbonation of soft drinks, as
Shielding gas during welding processes, in Synthesis of urea, dry ice, and other organic
synthesis. Carbon Dioxide poisoning is generally Accidental in nature like worker working in
deep well, dampen pit, overcrowding in ill-ventilated room etc.
4.3 Methyl Isocyanate (LC50 = 22 ppm)
Methyl Isocyanate (MIC) is one of a group of Isocyanates, the others being toluene di-
isocyanate (TDI) and diphenylmethane di-isocyanate (MDI). Methyl Isocyanate is a
colourless liquid with pungent sweetish odour below 27°C but it becomes gas at 39°C. It is a
highly volatile and inflammable in nature. It is an extremely reactive chemical and needs to
be stored carefully. Its contact with water results in an exothermic reaction. Methyl
isocyanate is produced by heating metal cyanates or by heating N, N-diphenyl-N’-
methylurea. Methyl Isocyanate is generally used in the manufacture of carbamate pesticide
and polyurethane articles like plastics, urethane foam, adhesives, etc. Methyl Isocyanate
causes carbamylation at biochemical level Methyl Isocyanate is a powerful respiratory
irritant. Even brief exposure at high concentrations may cause severe injury, burns, or even
death.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
4.4 Hydrogen Sulphide (LC50 = 712 ppm)
Hydrogen sulphide is in general referred as Sewer Gas and a well-known neurotoxic leading
to olfactory nerve paralysis and loss of consciousness at a relatively low dose. Hydrogen
sulphide is a colourless, toxic and flammable gas. It is responsible for the foul odour of rotten
eggs and pretentiousness. It is formed during decomposition of organic substances containing
sulphur. Hydrogen Sulphide readily diffuses through the tissues. The toxicity of Hydrogen
sulphide is similar with that of hydrogen cyanide. It forms a complex bond with iron in the
mitochondrial cytochrome enzymes, thereby blocking oxygen from binding and stopping
cellular respiration. It acts as a cytochrome oxidase poison, blocking the electron transport
chain those catalyses the reduction of molecular oxygen to water. Although very pungent at
first, it quickly reduces the sense of smell, so potential victims may be unaware of its
presence until it is too late resulting to accidental deaths. In Hydrogen Sulphide poisoning
putrefaction of dead body is rapid.
4.5 Aliphatic Hydrocarbons
Ethane is an odourless gas which is used as a refrigerant and as a component of natural gas. It
is methane, also known as Swamp Gas, however, which is the major component of natural
gas. Both are odourless gases and produce simple asphyxiation at high concentrations.
Conversion of domestic gas from coal gas (mostly carbon Monoxide) to natural gas (mostly
methane) has significantly reduced mortality from domestic gas leaks, since methane is much
less toxic as compared to Carbon Monoxide. Methane being odourless, a stenching agent
(alkyl mercaptan) is deliberately added to domestic gas so that leaks can be immediately
recognised. It is important to remember that a build-up of methane resulting in 4.8 to 13.5%
concentration in air constitutes an explosive mixture which can be ignited by a flame or even
a tiny spark. Most explosions in mines as well as homes using natural gas as fuel occur
because of this reason. Butane, Liquefied Petroleum Gas, propane, and propylene have a faint
petroleum-like odour and may be stenched with mercaptans for transport and storage. Butane
is often abused by adolescents in the form of inhalation. Liquefied petroleum gas is used as a
domestic, industrial, and automotive fuel. Propylene is a raw material in polypropylene,
isopropyl alcohol, isopropylbenzene, acetone, and propylene oxide manufacturing. Most of
the aliphatic hydrocarbon gases act as simple asphyxiants, in addition to additional specific
toxicities.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
4.6 Ammonia (LC50 = 4,000 ppm)
Ammonia is a colourless gas with pungent odour. It condenses to a liquid at 33.4°C. The
chemical formula is NH3. It is an extremely irritant gas with a penetrating odour. It is highly
water soluble forming ammonium hydroxide which is an alkaline corrosive. Aqueous
ammonia is a colourless liquid with a strong alkaline reaction (pH 11.6) and a penetrating
pungent odour. When heated to decomposition, it emits toxic fumes of ammonia and oxides
of nitrogen. While poisoning with ammonia is not very common, most of the cases reported
are suicidal in nature. Since the solution or gas even when weak has a distinct irritant smell,
accidental poisoning is unlikely. Obviously, its properties preclude its choice for murder.
However, ammonia is being used as a spray to incapacitate victims of robbery. Accidental
poisoning is common as it is mistaken for medicines, however, homicidal poisoning are rare.
Poisoning by inhalation of ammonia vapour is common. Sometimes caustic soda is thrown
over the face and body producing chemical burns.
4.7 Phosgene (LC50 = 5 ppm)
Phosgene is a colourless gas, heavier than air, with an odour of freshly-cut hay. At high
concentrations, the gas has an odour described as suffocating, strong, stifling, or pungent. At
low temperature or when compressed, phosgene condenses to a colourless to light yellow,
non-combustible, highly toxic, fuming/volatile liquid that produces poisonous vapour and
sinks in water. Phosgene is hydrolysed in the body to hydrochloric acid which produces a
systemic inflammatory response. It also stimulates the synthesis of lipoxygenase-derived
leukotrienes causing pulmonary oedema. Further, phosgene increases pulmonary vascular
permeability, leading to increased fluid accumulation in the interstitial and alveolar
compartments. The ability of the lymphatics to clear the excess fluid is exceeded, resulting in
gas diffusion abnormalities and pulmonary oedema. Phosgene was used as part of chemical
warfare during World War I. Prepared for the first time in 1812, phosgene had a large scale
presence in World War I as an asphyxiant war gas.
4.8 Phosphine (LC50= 20 ppm)
Phosphine is also known as Hydrogen phosphide or Phosphoretted hydrogen. It is a
colourless, flammable gas with an odour of garlic or decaying fish. Phosphine is commonly
used as a Fumigant, Grain preservative in the form of aluminium phosphide, Rat poison in
the form of zinc phosphide.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
Phosphine produces widespread organ damage due to cellular hypoxia as a result of binding
with cytochrome oxidase, an important respiratory enzyme. The organs with the greatest
oxygen requirements appear to be especially sensitive to damage and include the brain,
kidneys, heart, and liver. Phosphine when inhaled by human beings results in severe
pulmonary oedema. Due to the release of phosphine gas in contact with moisture, symptoms
of severe gastrointestinal tract irritation are produced that cause cardiovascular collapse and
death. Suicidal poisoning is common with this agent, especially in the northern part of India.
Rarely accidental poisoning may occur to workers working in grain elevators, ware houses
and grain freighter etc. Phosphine when it comes in contact with air and moisture. It reacts
with acidic media (HCL) of stomach and release phosphine gas, which is rapidly absorbed
from gastrointestinal tract by simple diffusion. Phosphine is a protoplasmic poison interfering
with enzymes and protein synthesis. In animal studies, phosphine has been shown to cause
non-competitive inhibition of cytochrome oxidase of myocardial mitochondria.
4.9 Hydrogen Cyanide (LC50 = 40 ppm)
Salts of cyanide releases hydrogen cyanide in stomach due to action of hydrochloric acid and
then absorbed as cyanide ion (CN-).Cyanide occurs as a gas or liquid or solid. In its gaseous
state it is referred to as Hydrogen Cyanide (HCN). Hydrogen cyanide is a colourless
flammable gas with a faint bitter almond odour. Hydrogen cyanide is occasionally used for
fumigation (ships, greenhouses), deaths can occur from negligence. Industrial and laboratory
mishaps involving this chemical are also not infrequent. Cyanogen and cyanogen halides
(cyanogen bromide, cyanogen chloride, and cyanogen iodide) release hydrogen cyanide and
have been used as military chemical warfare agents. During the First World War, HCN was
used as a war gas but was quickly replaced by other more effective war gases such as
Mustard Gas.
4.10 Chlorine (LC50= 293 ppm)
Chlorine is a greenish-yellow gas with a pungent odour. Chlorine is not found free in nature
due to its reactivity with other chemicals. Instead, it is found as sodium chloride in land-
locked lakes, as rock salt in underground deposits, in brines, and in natural deposits of Sylvite
and Carnallite. Chlorine is an extremely active oxidising agent and causes rapid and extensive
destruction of organic tissue. It combines with tissue water to produce HCl, producing injury
and reactive oxygen species. Swimming pool chlorinator tablets or pellets may result in
chlorine gas exposure.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
Chlorine is used to manufacture a number of chemicals including solvents such as carbon
tetrachloride, trichloroethylene, tetrachloroethylene, and methylene chloride, pesticides and
herbicides, plastics, vinyl chloride, etc. It is also used in making refrigerants and propellants
such as halocarbons and methyl chloride. It is used extensively in pulp mills, where wood
chips are processed into pulp as part of the paper manufacturing process. Chlorine is also
employed in purifying drinking and swimming water, for sanitation of industrial and sewage
wastes and other disinfecting uses. It has been used as a poisonous gas for military purposes
under the name Bertholite. Most cases of poisoning are accidental arising out of domestic or
industrial exposure. Sometimes, exposure occurs at swimming pools where chlorine is often
used as a disinfectant.
5. Warfare Gases
War gases are the agents used to kill, injure or incapacitate the enemies. In civil conditions,
these gases are used to disperse the unruly mob. The history of war gases begins with First
World War where more than 100,000 people died and about 1.2 million affected due to use of
chlorine, phosgene, and nitrogen mustard. In Second World War, the Germans developed and
used number of nerve agents like Tabun, Sarin and Soman, together referred as “G” military
agents whereas the English developed VX (Nerve Gas) in 1952.
Classification of Warfare Gases:
5.1 Lachrymators (Tear Gas): Chloracetophenon (CAP), Bromo benzyl cyanide (BBC),
Ethyl-iodo-acetate (KSK).
5.2 Lung irritants: Chlorine, Phosgene, Diphosgene, etc.
5.3 Vesicants: Mustard gas, Lewisite.
5.4 Sternutators: Diphenylamine chlorarsine (DM), Diphenyl chlorarsine (DA), Diphenyl
cyanarsine (DC), etc.
5.5 Paralysants: Carbon Monoxide, Hydrogen Sulphide.
5.6 Nerve gases: Tabun, Sarin, Soman, and VX.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
6. Forensic Analysis of some Poison Gases
Basically, Gaseous Poisons are isolated by the distillation process or, more usually, by
sampling the headspace above the sample held in a closed container. Besides other methods
are discussed below:
6.1 Conway Micro Diffusion technique
Conway micro diffusion assembly is of a brink type, polypropylene cells with clear
polystyrene covers having an outermost annular sealing well, an intermediate annular well for
the sample and the liberating agent and a center well for the reagent (detection reagent) which
is used to trap the diffusing gas or vapour.
Poison Sealing/Liberating
Agent Absorbent/ reactant Detection
Carbon
Monoxide
10% Sulphuric
acid
Palladium chloride
solution (0.5%) in 2N
HCl-acts as detection
reagent.
Palladium Chloride
solution turns grey to
black.
Cyanide 10% Sulphuric
acid
10% NaOH solution
(absorb HCN gas).
Alkaline extract is
subjected to Prussian
blue test using FeSO4
and HCl – Prussian
blue ppt. or
colouration.
Sulphur
Dioxide
10% H2SO4 10% NaOH Formation of black
ppt with lead acetate.
6.2 Test for detection of Phosphine
5 to 10 ml amount of gastric extract or 5 to 10 gm of macerated tissue of liver is taken into a
steam distillation flask to which an equal quantity of water is added and then acidified with
dilute Hydrochloric Acid or Sulphuric Acid, followed by heating up to 50°C for 15 minutes.
The distillate is collected in an ice cold receiver containing 5 ml of 1% Silver Nitrate solution
by dipping the adapter into it. If phosphine is present, the solution will turn black. For
confirmation, 5 ml of concentrate Nitric Acid is added to the black precipitate and boiled till
the solution becomes clear. Then 5 ml of Ammonium Molybdate solution is added and heated
for one minute. Formation of yellow precipitate confirms the presence of phosphine.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
A variation of this test involves placing Lead Acetate (0.1 N) filter paper over the mouth of
the distillation flask containing the sample (prepared in the same manner as detailed above).
The flask is heated for 15 minutes at 50oC. Phosphine will blacken the silver nitrate paper,
while Hydrogen Sulphide will blacken both papers.
6.3 Carbon Monoxide detection in blood
Two small porcelain-evaporating dishes are taken and 1 ml of normal blood into one dish and
1 ml of suspected blood in another dish is decanted. Both the dishes are heated gradually.
The normal blood will change to a brown black whereas the blood having Carbon Monoxide
will become brick red. This test is sensitive to 40% carbon Monoxide.
In another test, a drop of test sample blood is diluted with 10-15 ml of water. Control sample
blood is also diluted in the same manner. Blood containing carbon Monoxide is pink. This
test is sensitive to 50% carbon Monoxide.
7. Summary
Asphyxiants are gases that cause tissue hypoxia which means they are gases that deprive
body tissues of oxygen.
Carbon dioxide (CO2) is a colourless, odourless, non- irritating gas that is widely used as
a fire extinguisher, in ice-making factories and occupational or recreational (diving)
settings.
Cyanides (CN-) are utilized in mining operations, photographic materials, the production
of plastics, pigments, and dyes, and often used as fumigant pesticides. During fires,
victims can also inhale significant carbon Monoxide and cyanide gases, which may cause
synergistic toxicity in humans
Methyl Isocyanate (MIC) was involved in one of the most devastating gas disasters,
which occurred in Bhopal, Madhya Pradesh in 1984, leaving more than 2000 people dead,
and more than 200,000 injured. The incident occurred in a pesticide division of Union
Carbide Company manufacturing Carbaryl (a carbamate), for which methyl isocyanate is
required. This deadly chemical was stored in huge, double walled stainless steel tanks,
one of which burst on the night of December 2, 1984.
FORENSIC SCIENCE
PAPER No. 10: Forensic Toxicology
MODULE No. 18: Poisonous Gases
More than 24,000 kg of MIC gas escaped over the next several hours into the atmosphere
forming an ominous white cloud that floated rapidly over the surrounding heavily
populated neighbourhood killing thousands in their sleep and incapacitating several
thousands more.
Butane is used as a raw material for automobile fuels, in organic synthesis, and as a
solvent, refrigerant, and aerosol. Propane is used as a raw material in organic synthesis, as
a component of industrial and domestic fuels, as an extractant, as a solvent, as a
refrigerant, and in the manufacture of ethylene. Incomplete combustion of these agents
can release Carbon Monoxide into the ambient air.
Ammonia has greater tendency than other alkalis to penetrate and damage the iris, and to
cause burns and cataracts in cases of severe exposure. Mixing of ammonia with
hypochlorite bleach, results in the formation of chloramine, which causes a toxic
pneumonitis (pulmonary oedema).
Accidental and suicidal poisonings due to Phosphine have been reported involving the
consumption of rat pastes containing zinc phosphide. Some of these brands are marketed
in tubes that look very similar to toothpaste tubes leading to accidental use.