CHAPTER ONE

INTRODUCTION

1.1 Background of Study

Gas detection system is used for the control of hazardous liquefied petroleum gas and other gases in an environment. People have worked in hazardous atmospheres before the development of Gas detection system. The open flame light sources of pre-historic cave painters were sources of potentially deadly carbon monoxide and consumers of life giving oxygen and in a poorly ventilated area could have eventually proved fatal. Often the potential toxicity of the environment was only poorly recognized, if it was recognized at all. Fatalities and injuries were accepted as a risk of doing the job, or the tasks were given to unwilling workers under armed guard. Some of the first attempts to detect toxic atmospheres came in coal mines. Coal mines are notorious sources of combustible and toxic gases as well as low oxygen levels. Open flame lamps served as some of the first detection systems. A low oxygen environment would cause the flame to burn low, or become extinguished. An atmosphere rich in combustible gases would cause the flame to burn more brightly. However, too much combustible gas resulted in the very explosion that was trying to be avoided. A later improvement on this method was the flame lamp, which contained the flame inside a glass barrel and allowed the hot gases to escape through a flame arresting wire mesh. Graduating marks were placed on the glass to allow a rough calculation of the presence of combustible gas or the absence of oxygen. While this method greatly improved the intrinsic safety of this detection method, a dropped lamp could still prove fatal in the wrong environment.

Another attempt at an intrinsically safe detection method was also used in coal mining applications into the twentieth century. This was the use of small caged birds to detect toxic environments (the proverbial ‘canary in a coal mine’). The concept was that these birds would exhibit the effects of the toxic environment before they became injurious to humans. As you can imagine, a healthy bird at the beginning of the work period was a vital requirement. While effective in certain applications, these birds were not capable of detecting all hazardous conditions. In the 1920's a number of significant advancements in the field of gas detection came into play. In Japan Dr. Jiro Tsuji developed a method of detecting combustible gases using light-wave interference in 1925. Dr. Tsuji later went on to found Riken Keiki Co., Ltd, currently represented in North America by RKI Instruments. In 1927 Dr. Oliver Johnson of the Standard Oil Company developed a method of detecting combustible gases using a platinum catalyst in a Wheatstone bridge electronic circuit. Dr. Johnson later went on to found Johnson-Williams or J-W, one of the first gas detection companies in the United States. Since the 1920's a number of advancements have been made in these two technologies. In addition, a number of other technologies like MQ-6 gas sensor have also come into use and today it is used in this project work. The MQ-6 gas sensor is made up of SnO2 which has lower conductivity in clean air. A simple electro-circuit is used here which is used to convert the changing conductivity into corresponding output signal of gas concentration. Both methane and propane can be detected easily by MQ-6 sensor because it has high sensitivity towards Methane, Propane and Butane. It is a low cost sensor suitable for different applications.

1.2   Problem Statement

Gas detectors are an essential application for home and commercial safety; they are also employed in numerous industrial industries. They are used in welding shops to detect combustibles and toxics and in nuclear plants, to detect combustibles. They are also commonly used to detect hazardous vapors in wastewater treatment plants and are very efficient in confined spaces where there is no continuous employee occupancy. Such spaces include tanks, pits, vessels and storage bins. They may also be placed at a site to detect toxins prior to occupant entry where it commonly used for gas leak detection system, fire/safety detection system and gas leak alarm. It can be found in a variety of locations such as on oil rigs to monitor manufacture processes and emerging technologies such as photovoltaic. They may also be used in firefighting. Typical installation areas being gas yards (Bullets), gas banks with multi cylinders in manifold, user production departments/utility areas like kitchens.  Other areas of application and the common gases it can detect are listed in the table below:

        TABLE 1.2 Common Gasses and Detection Applications

Application 

Common Gases Detected

Water & Waste Water Treatment

chlorine, hydrogen sulfide, methane, oxygen

Petroleum Production & Refining

hydrogen sulfide, combustible gases

Natural Gas Production & Transport

natural gas, hydrogen sulfide, mercaptans

Mining

methane, oxygen, dust

Gold Extraction

hydrogen cyanide

Electroplating

hydrogen cyanide

Food Processing & Cold Storage

chlorine, ammonia, methane, dust

Grain Storage & Transportation

methane, oxygen, phosphine, dust

Breathing Air (Supplied Air Systems)

carbon monoxide, oxygen

Parking Garages

carbon monoxide

Semiconductor Manufacturing & Processing

arsine, phosphine, silane, hydrogen,

hydrochloric acid, numerous other gases

Fuel Storage & Transportation

combustible gases, oxygen

Leaking Underground Storage Tanks

combustible gases, oxygen

Pulp & Paper Manufacturing

chlorine, chlorine dioxide, hydrogen sulfide, sulfur dioxide, oxygen

Beer & Wine Making

oxygen, carbon dioxide, sulfur dioxide

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