ECH3602

SAFETY AND RISK ASSESSMENT

Fundamentals of Fires and Explosions

Group Members:

Nur Shafiqah Binti Md Samsuri 161578

Nor Azlita Binti Abu Bakar 161864

Nurfadzilah Binti Ibrahim 162382

Areej Abdul Majeed Shah Redha Al Bulushi 171632

Lecturers Name:

Assoc Prof Dr Mohd Halim Shah Bin Ismail

1. What is the flash point of a liquid?

Flash point of a liquid is the lowest temperature at which it gives off enough vapour to

form an ignitable mixture with air.

2. What is the fundamental difference between flammable and combustible stock?

Flammable Stock Combustible Stock

Capable of being ignited without having

to be heated.

Needed to be heated by external sources

in order to be capable of burning.

3. What is the cut off point between a flammable liquid and a combustible liquid as

defined by the NFPA standards?

Flammable Stock Combustible Stock

Flash points below 100F (38C) and a

vapour pressure below 40 psi.

Flash points at or above 100F (38C).

4. What is the difference between the terms lower explosive limit (LEL) and lower

flammable limit (LFL)?

There is no difference between the terms LEL and LFL. These two terms convey the

same meaning.

5. A material whose flash point is 212F (100C) is being stored at 203F (95C). Is this

treated as a flammable or combustible material under ExxonMobil practices?

The material will be treated as combustible material. This is because it is stored

within 15F (10C) of its flash point.

6. There is a correlation of flash point with upper flammable limit (UFL) by means of

the vapour pressure curve.

False. The correlation is between flash point and lower flammability limit (LFL).

7. A pipe whose surface temperature is 662F (350C) represents a likely source of

ignition for a flammable vapour whose auto-ignition temperature (A.I.T.) is 608F

(320C).

False. The surface temperature of the pipe should be at least 220F (105C) higher

than the A.I.T. for an ignition source.

8. Pressure has a significant effect on the flammable range of most hydrocarbons.

True. Flammable range expands as the pressure increase.

9. Deflagration is another word for detonation.

False. Deflagration is an explosion in which the reaction front moves at a speed less

than the speed of sound in the unreacted medium (sub-sonic velocities). Detonation is

an explosion in which the reaction front moves at a speed greater than the speed of

sound in the unreacted medium (supersonic velocities).

10. Typical pressures reached in a confined deflagration are 6 to 8 times the initial

pressure.

True. The rate of pressure increase indicate the flame front propagation rate and thus

the magnitude of explosion.

11. Stoichiometric mixtures generally require higher ignition energies than other mixtures

within the flammable range.

False. Stoichiometric mixtures require lower ignition energies than other mixtures

within the flammable range.

12. The only factors that determine the strength of a vapour cloud explosion are the type

of molecule and the amount released.

False. The other factors that determine the strength of a vapor cloud explosions are

confinement, weather, and source consideration.

13. The TNT model is still the best for modelling explosions.

False. The Multi-Energy Method (MEM) has been developed, which is an alternative

to the TNT model and is considered to be more accurate.