Fire, Arson and Explosives Questions and Answers

Q: Which of the following is a poor water resistance explosive ?

The explosive with poor water resistance is poured ANFO.ANFO is ammonium nitrate prills mixed with about 6% fuel oil. Ammonium nitrate is very soluble in water, so loose ANFO poured into a wet borehole dissolves and fails to detonate. That is why it is used only in dry holes.Packaged ANFO is sealed in plastic and can be used where there is some water. Emulsion explosives have the nitrate solution locked inside an oil phase, and gelatin dynamite contains nitroglycerine gelled with nitrocellulose; both are known for good water resistance.

Q: The boiling point of any petroleum product depends on :

The boiling point of a petroleum product depends on the number of carbon atoms.Petroleum products are mixtures of hydrocarbons. As the carbon chain grows, the molecules become larger and the van der Waals forces between them stronger, so the boiling point rises. This is the basis of fractional distillation: gases (C1-C4) come off first, then petrol, kerosene, diesel and heavier fractions.Hydrocarbons contain no oxygen, and water is a contaminant, not a determinant of a fraction's boiling range. All the constituents are organic, so 'presence of organic constituents' cannot distinguish one product from another.

Q: The petroleum product having more than \(\text{C}_{50}\) will be known by :

The key gives coke for the fraction above \(\text{C}_{50}\).In the usual table of petroleum fractions by carbon number, the lightest products are gases and naphtha (roughly C5-C10), followed by kerosene, diesel, lubricating oils and waxes in the C20-C40 range. Material heavier than about C50 stays as the distillation residue, from which bitumen and petroleum coke are produced.Naphtha is a light fraction, wax lies below C50, and gel is not a petroleum fraction, so of the options only coke belongs to the heaviest residue.

Q: Rate of charring of wood depends on all, except :

The rate of charring does not depend on the demarcation line.How fast wood chars depends on the intensity of the fire (the heat reaching the surface), the duration of exposure, and the moisture content of the wood, along with its species and density. Fire investigators use the depth of char to compare how long and how hot different areas burned.A line of demarcation is the boundary between charred and uncharred material. It is a result of burning that investigators read to trace fire spread, not a factor that controls the charring rate.

Q: Distortion of glass article on fire suggests that the temperature reached :

Distortion of glass indicates a temperature of 750°C to 850°C.Ordinary soda-lime glass has no sharp melting point; it softens progressively once it passes its softening point of a little over 700°C. Fire investigators therefore read the condition of glass articles as a rough thermometer, and distortion or sagging of a glass article points to the band of about 750 to 850°C that the key gives.Below that range glass may crack from thermal stress without losing its shape, and at 1000°C and above it would be melted into a flowing mass rather than merely distorted.

Q: Which of the following explosive is the lowest density ?

The lowest density explosive is ANFO.ANFO is a mixture of porous ammonium nitrate prills with about 6 percent fuel oil. Poured loose, it has a bulk density of only about 0.8 to 0.9 g/cm\(^{3}\), which is why it is used in large quantities to fill boreholes in mining and quarrying.Dynamite has a density of roughly 1.2 to 1.5 g/cm\(^{3}\), and the military high explosives PETN and RDX are much denser, at about 1.7 to 1.8 g/cm\(^{3}\) as crystals. High density is one reason the military explosives detonate faster and more violently.

Q: Which of the following detonating device uses a primary explosive ?

The device that uses a primary explosive is the electric blasting cap.An electric blasting cap contains a bridge wire that heats when current flows, igniting a small charge of a primary explosive such as lead azide or lead styphnate. The primary explosive detonates from that small stimulus and in turn sets off the base charge (a secondary explosive such as PETN) and then the main charge.An exploding bridgewire detonator is designed specifically to work without any primary explosive: a large, fast current pulse vaporises the wire and initiates a secondary explosive directly, which makes it much safer. Detonating cord carries secondary explosive, and a 'novel card' is not an initiating device.

Q: Dynamite is manufactured with the help of :

Dynamite is manufactured with nitroglycerine.Alfred Nobel invented dynamite in 1867 by absorbing liquid nitroglycerine, which is dangerously sensitive to shock, into an absorbent material, originally kieselguhr (diatomaceous earth). This made the explosive far safer to handle and transport while keeping its power.Mercury fulminate is a primary explosive used in detonators, not the body of dynamite. Ammonium nitrate and sodium or potassium nitrate are used in some later 'ammonia' dynamites and in black powder, but the defining ingredient of dynamite is nitroglycerine.

Q: Collection of fire debris at crime scene cannot be accomplished by packing in airtight container with :

The material that is not used is carbonate strips.Fire debris suspected to contain ignitable liquid residues is sealed in airtight containers (metal cans, glass jars or nylon bags) to stop the volatiles escaping. The residues are then recovered from the headspace by adsorption onto a suitable adsorbent: activated charcoal strips (passive headspace concentration, as in ASTM E1412), Tenax, a porous polymer, or adsorption tubes packed with such materials, which are later desorbed with solvent or heat for GC-MS analysis.Carbonate strips are not an adsorbent for hydrocarbons and play no part in fire debris sampling, so they are the odd one out.

Q: Which of the following dye is added to petrol to give color to it ?

The key's answer is phenyl azo 2-naphthol. I could not confirm in a source which dye is added to petrol in India, so this follows the key.Phenyl azo 2-naphthol (1-phenylazo-2-naphthol) is the azo dye known as Sudan I, an orange-red, oil-soluble dye, which is the kind of colourant that dissolves in a hydrocarbon fuel. Sudan II, option D, is a different azo dye (a xylyl-azo-naphthol), so the two are separated only by knowing which one the fuel trade actually uses.Di-alkyl amino anthraquinone belongs to the anthraquinone dyes, a different class from the azo dyes, and alizarin yellow is a water-soluble mordant-type azo dye, a poor fit for a fuel.

11.

Which of the following is a poor water resistance explosive ?

A.Gelatin dynamite
B.Cartridge emulsion
C.Poured ANFO
D.Packaged ANFO

Exam Year(s)

MH SET - 2019, MH SET - 2021, SET Exam - 2019, SET Exam - 2021,

Answer: C

The explosive with poor water resistance is poured ANFO.

ANFO is ammonium nitrate prills mixed with about 6% fuel oil. Ammonium nitrate is very soluble in water, so loose ANFO poured into a wet borehole dissolves and fails to detonate. That is why it is used only in dry holes.

Packaged ANFO is sealed in plastic and can be used where there is some water. Emulsion explosives have the nitrate solution locked inside an oil phase, and gelatin dynamite contains nitroglycerine gelled with nitrocellulose; both are known for good water resistance.

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12.

The boiling point of any petroleum product depends on :

A.Presence of water molecule
B.Number of oxygen atoms
C.Presence of organic constituents
D.Number of carbon atom

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The boiling point of a petroleum product depends on the number of carbon atoms.

Petroleum products are mixtures of hydrocarbons. As the carbon chain grows, the molecules become larger and the van der Waals forces between them stronger, so the boiling point rises. This is the basis of fractional distillation: gases (C1-C4) come off first, then petrol, kerosene, diesel and heavier fractions.

Hydrocarbons contain no oxygen, and water is a contaminant, not a determinant of a fraction's boiling range. All the constituents are organic, so 'presence of organic constituents' cannot distinguish one product from another.

Discuss in Forum

13.

The petroleum product having more than \(\text{C}_{50}\) will be known by :

A.Naphtha
B.Wax
C.Gel
D.Coke

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The key gives coke for the fraction above \(\text{C}_{50}\).

In the usual table of petroleum fractions by carbon number, the lightest products are gases and naphtha (roughly C5-C10), followed by kerosene, diesel, lubricating oils and waxes in the C20-C40 range. Material heavier than about C50 stays as the distillation residue, from which bitumen and petroleum coke are produced.

Naphtha is a light fraction, wax lies below C50, and gel is not a petroleum fraction, so of the options only coke belongs to the heaviest residue.

Discuss in Forum

14.

Rate of charring of wood depends on all, except :

A.Intensity of fire
B.Duration of exposure
C.Moisture content
D.Demarcation line

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

The rate of charring does not depend on the demarcation line.

How fast wood chars depends on the intensity of the fire (the heat reaching the surface), the duration of exposure, and the moisture content of the wood, along with its species and density. Fire investigators use the depth of char to compare how long and how hot different areas burned.

A line of demarcation is the boundary between charred and uncharred material. It is a result of burning that investigators read to trace fire spread, not a factor that controls the charring rate.

Discuss in Forum

15.

Distortion of glass article on fire suggests that the temperature reached :

A.Below 750°C
B.750°C to 850°C
C.1000°C to 1500°C
D.1500°C to 2000°C

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: B

Distortion of glass indicates a temperature of 750°C to 850°C.

Ordinary soda-lime glass has no sharp melting point; it softens progressively once it passes its softening point of a little over 700°C. Fire investigators therefore read the condition of glass articles as a rough thermometer, and distortion or sagging of a glass article points to the band of about 750 to 850°C that the key gives.

Below that range glass may crack from thermal stress without losing its shape, and at 1000°C and above it would be melted into a flowing mass rather than merely distorted.

Discuss in Forum

16.

Which of the following explosive is the lowest density ?

A.ANFO
B.Dynamite
C.PETN
D.RDX

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: A

The lowest density explosive is ANFO.

ANFO is a mixture of porous ammonium nitrate prills with about 6 percent fuel oil. Poured loose, it has a bulk density of only about 0.8 to 0.9 g/cm\(^{3}\), which is why it is used in large quantities to fill boreholes in mining and quarrying.

Dynamite has a density of roughly 1.2 to 1.5 g/cm\(^{3}\), and the military high explosives PETN and RDX are much denser, at about 1.7 to 1.8 g/cm\(^{3}\) as crystals. High density is one reason the military explosives detonate faster and more violently.

Discuss in Forum

17.

Which of the following detonating device uses a primary explosive ?

A.Detonating card
B.Novel card
C.Exploding Bridgewire Detonators
D.Electric Blasting caps

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

The device that uses a primary explosive is the electric blasting cap.

An electric blasting cap contains a bridge wire that heats when current flows, igniting a small charge of a primary explosive such as lead azide or lead styphnate. The primary explosive detonates from that small stimulus and in turn sets off the base charge (a secondary explosive such as PETN) and then the main charge.

An exploding bridgewire detonator is designed specifically to work without any primary explosive: a large, fast current pulse vaporises the wire and initiates a secondary explosive directly, which makes it much safer. Detonating cord carries secondary explosive, and a 'novel card' is not an initiating device.

Discuss in Forum

18.

Dynamite is manufactured with the help of :

A.Mercury fulminate
B.Nitroglycerine
C.Ammonia nitrate
D.Potassium nitrate

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: B

Dynamite is manufactured with nitroglycerine.

Alfred Nobel invented dynamite in 1867 by absorbing liquid nitroglycerine, which is dangerously sensitive to shock, into an absorbent material, originally kieselguhr (diatomaceous earth). This made the explosive far safer to handle and transport while keeping its power.

Mercury fulminate is a primary explosive used in detonators, not the body of dynamite. Ammonium nitrate and sodium or potassium nitrate are used in some later 'ammonia' dynamites and in black powder, but the defining ingredient of dynamite is nitroglycerine.

Discuss in Forum

19.

Collection of fire debris at crime scene cannot be accomplished by packing in airtight container with :

A.Adsorption tubes
B.Charcoal strips
C.Tenax
D.Carbonate strips

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: D

The material that is not used is carbonate strips.

Fire debris suspected to contain ignitable liquid residues is sealed in airtight containers (metal cans, glass jars or nylon bags) to stop the volatiles escaping. The residues are then recovered from the headspace by adsorption onto a suitable adsorbent: activated charcoal strips (passive headspace concentration, as in ASTM E1412), Tenax, a porous polymer, or adsorption tubes packed with such materials, which are later desorbed with solvent or heat for GC-MS analysis.

Carbonate strips are not an adsorbent for hydrocarbons and play no part in fire debris sampling, so they are the odd one out.

Discuss in Forum

20.

Which of the following dye is added to petrol to give color to it ?

A.Phenyl azo 2-naphthol
B.Di-alkyl amino anthraquinone
C.Alizarin yellow
D.Sudan II

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: A

The key's answer is phenyl azo 2-naphthol. I could not confirm in a source which dye is added to petrol in India, so this follows the key.

Phenyl azo 2-naphthol (1-phenylazo-2-naphthol) is the azo dye known as Sudan I, an orange-red, oil-soluble dye, which is the kind of colourant that dissolves in a hydrocarbon fuel. Sudan II, option D, is a different azo dye (a xylyl-azo-naphthol), so the two are separated only by knowing which one the fuel trade actually uses.

Di-alkyl amino anthraquinone belongs to the anthraquinone dyes, a different class from the azo dyes, and alizarin yellow is a water-soluble mordant-type azo dye, a poor fit for a fuel.

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