USAutomatic Fire and Security

At USAutomatic, we are committed to providing a complete range of fire detection solutions and services. We strive to help others better understand the impact and benefits of various types of fire detection technologies.

Inevitably occasional escapes of gas occur, which create a potential hazard to the industrial plant, its employees and people living nearby. Worldwide incidents, involving asphyxiation, explosions and loss of life are a constant reminder of this problem.

Gas Hazards

There are three main types of gas hazard:

Flammable:		Risk of fire and/or explosion (230 or more known flammable gases. e.g. Methane, Butane, Propane, etc).
Toxic:		Risk of Poisoning (60 plus known toxic gases. e.g. Carbon Monoxide, Hydrogen Carbon Dioxide, Chlorine, etc).
Asphyxiant:		Risk of Suffocation (e.g. Oxygen deficiency). Oxygen can be consumed or displaced by another gas.

Flammable Gas Hazards

Combustion is a fairly simple chemical reaction in which oxygen is combined rapidly with another substance resulting in the release of energy. This energy appears mainly as heat – sometimes in the form of flames. The igniting substance is normally, but not always, a Hydrocarbon compound and can be solid, liquid, vapor or gas. There are approximately 234 known flammable gases.

Toxic Gas Hazards

Some gases are poisonous and can be dangerous to life at very low concentrations. Some toxic gases have strong smells like the distinctive ‘rotten eggs’ smell of H₂S. The measurements most often used for the concentration of toxic gases are parts per million (ppm) and parts per billion (ppb). The term ‘hygiene monitoring’ is generally used to cover the area of industrial health monitoring associated with exposure of employees to hazardous conditions of gases, dust, noise etc. In other words, the aim is to ensure that levels in the workplace are below the statutory limits.

Asphyxiant (Oxygen Deficiency) Hazard

Oxygen depletion can be caused by displacement, combustion, oxidation or chemical reaction.

Oxygen Enrichment Hazard

Oxygen enrichment can also cause a risk. At increased O₂ levels the flammability of materials and gases increases. If too high, items such as clothing can spontaneously combust. Areas where hazards may arise from oxygen enriched atmospheres include welding equipment, manufacturing, storing rocket propulsion systems, products used for bleaching in the pulp and paper industry and clean water treatment facilities.

Typical Areas that Require Gas Detection

Oil & Gas

Semiconductor Manufacturing

•	Exploration Drilling Rigs
•	Production Platforms
•	Onshore Oil and Gas Terminals
•	Refineries

•	Water Reactor
•	Water Dryers
•	Gas Cabinets
•	Chemical Vapor Deposition

Boiler Rooms

Power Stations

•	Flammable Gas Leaks from the Incoming Gas Main
•	Leaks from the Boiler and Surrounding Gas Piping
•	Carbon Monoxide Given Off by Badly Maintained Boiler

•	Around the Boiler Pipe Work and Burners
•	In and Around Turbine Packages
•	In Coal Silos and Conveyor Belts in Older Coal/Oil Fired Stations

Tunnels/Car Parks

Waste Water Treatment Plants

•	Car Tunnels
•	Underground and Enclosed Car Parks
•	Access Tunnels
•	Ventilation Control

•	Digesters
•	Plant Sumps
•	Pumps
•	H₂S Scrubbers

Chemical Plants

Hospitals

•	Raw Material Storage
•	Process Areas
•	Laboratories
•	Pump Rows
•	Compressor Stations
•	Loading/Unloading Areas

•	Laboratories
•	Refrigeration Plants
•	Boiler Rooms

Gas Detection Techniques and Comparison

Gas	Advantages	Disadvantages
Catalytic	Simple, measures flammability of gases. Low cost proven technology.	Can be poisoned by lead, chlorine and silicones that remains an unrevealed failure mode. Requires oxygen or air to work. High power. Positioning critical.
Electrochemical	Failure modes are unrevealed unless advanced monitoring techniques used. Requires oxygen to work. Positioning critical.	Failure modes are unrevealed unless advanced monitoring techniques used. Requires oxygen to work. Positioning critical.
Point Infrared	Uses a physical rather than chemical technique. Less sensitive to calibration errors. No unseen failure modes. Can be used in inert atmospheres.	Flammable gas detection only in %LEL range. Measures concentration of flammable gases which have then to be related to the flammability of the gas. Positioning critical. High/medium power.
Open Path Infrared	Area coverage – best chance to see a leak. No unseen failure modes. Latest Technology. Can detect low concentrations. Positioning not as critical. New toxic version as well as flammable.	Higher initial purchase cost. Not suitable for use in smaller areas. Detection path can be obscured.
Semiconductor	Mechanically robust, works well in constant high humidity conditions.	Susceptible to contaminants and changes in environmental conditions. Non linear response effects complexity.
Thermal Conductivity	Measures %VN concentrations of binary gas mixtures even with the absence of oxygen.	High gas concentrations only. Limited range of gases. Cannot measure gases with conductivities close to air. Higher maintenance requirements.
Paper Type	Highly sensitive and selective for toxic gases. Leaves physical evidence of the gas exposure. No false alarms.	Requires extraction system. May need sample conditioning.