Zone Classification

Zone 0

An area in which an explosive gas/air mixture is continuously present, or present for long periods. Explosive atmosphere Present continuously >1000hrs/annum.

Zone1

An area in which an explosive gas/ air mixture is likely to occur in the normal operation of the plant. Explosive atmosphere Present intermittently >10 <1000Hrs/annum.

Zone 2
An area in which an explosive gas/ air mixture is not likely to occur in normal operation and if it is occurs, it is only for a short period of time. Explosive atmosphere present abnormally <10 hrs / annum.

Zone20 
An area in which a combustible dust, as a cloud, is present continuously or frequently during normal operations in sufficient quantities to produce an explosive mixture.

Zone 21

An area in which a combustible dust, as a cloud, is likely to occur during normal operations in sufficient quantities to produce an explosive mixture.

Zone 22 
An area in which combustible dust clouds may occur infrequently and persist for only short periods of time or in which accumulations or layers may be present under abnormal conditions.

What is Gas?.

An air like fluid substance which expands freely to fill any space available, irrespective of its quantity. Gases can move will mix rapidly into any atmosphere in which they are released.

Gas Hazards

There are three main types of gas hazard: Flammable, Toxic and Asphyxiant/Oxygen deficiency hazards.

Flammable gas hazards

Risk of fire and / or explosion e.g. Methane, Butane, and Propane

Toxic gas hazards

Risk of poisoning e.g. Hydrogen suphied (H2s), Carbon Monoxide, Chlorine

The measurements most often used for the concentration of toxic gases are parts per million (ppm) and parts per billion (ppb)

Asphyxiant/oxygen deficiency

Risk of suffocation e.g.  Oxygen deficiency. Oxygen can be consumed or displaced by another gas.Normal ambient air contains an oxygen concentration of 20.9% v/v. When the oxygen level dips below 19.5% v/v, the air is considered oxygen deficient. Oxygen concentrations below 16% v/v are considered unsafe for humans.

What is Fire?.

A process in which substances combine chemically with oxygen from the air and typically give out Light,Heat and Smoke.

Fire Triangle

Fire is a chemical process. Three elements are needed for this process: oxygen, heat and fuel. Without one of these elements a fire cannot start or continue. The fire is prevented or extinguished by removing any one of them. A fire naturally occurs when the elements are combined in the right mixture.

Fire and Gas System

Fire and Gas (F&G) system is a safety system which is designed to protect personnel,plant and environment from hazardous conditions.A Fire and Gas system continuously monitors hazardous conditions such as fire,combustible and toxic gas release with in the plant,and provides early warnings to personnel and initiate protective actions to prevent consequences of the incident.F&G systems can also interface with Emergency Shutdown (ESD) and tripping systems,HVAC control and automatic release of fire suppression systems.

Basically the system consists of field mounted detectors and manual alarm call  point,a system logic unit for processing of incoming signals and HMI, audible and visual alarm and fire suppression systems.The system is able to process all input signals in accordance with the applicable data sheets or cause and effect charts.

Field Mounted Detectors

The F&G system connected following various types of field mounted detectors for monitoring abnormal conditions and collect data from areas.

• Combustible/Flammable Gas detector
• Oxygen Deficiency detector
• Toxic Gas detector
• Flame/Fire detector (UV or UV/IR)
• Smoke detector
• Heat detector (rate of rise or fixed temperature detector)

Fire Suppression Systems

• Deluge system
• Carbon Dioxide (Co2) system
• FM 200
• Hi Expansion Foam system
• Rim Seal Fire Protections
• Inergen Fire Suppression system 
• Fire Monitors

Typical industrial application of the F&G systems include offshore/onshore oil and gas exploration and production facilities, refineries,petro-chemical plants, tank farms, storage areas, loading unloading operations and marine, power plant and mining operations.