1.1 HISTORY OF KITAGAWA GAS DETECTOR TUBES
The history of Kitagawa gas detector tubes goes back to 1946, when a study was undertaken to determine the efficiencies of desulfurisers in the production of ammonium sulphate, then used as a fertilizer. While ammonia, a raw material of ammonium sulphate,was produced by synthesizing hydrogen and nitrogen with theaid of a catalyst under high pressure, the catalyst was deteriorated by hydrogen sulphide mixed in the hydrogen as an impurity. It was determined that a new method of gas detection was needed for a process control environment.This new method would need to meet the following requirements : 1 Hydrogen sulphide can be measured with high accuracy. 2 The detector must be small and light enough to carry.3 The detector must be easy to operate, requiring no special skills. 4 Measurement results should be obtained fast, with no calculation required. 5 No liquid reagents were to be used. 6 The detector could not use electrical power to prevent possible gas/vapour explosion. In solving these strict requirements, the basic concept of the Kitagawa gas detector tube, using a dry chemical reaction, wasborn. The detector tube made use of the discolouration reaction of a detecting reagent lead acetate adsorbed on the surface of solid granules such as silica gel . Gas measurement was made by the colour change of the detecting reagent. As the hydrogen sulphide was passed through the thin glass detector tube filled with the white detecting reagent, the tube turned black, and the degree of thediscolouration increased in proportion to the hydrogen sulphide concentration. This new method was quickly adopted by a number of ammonia synthesis plants, where its performance was confirmed with as accuracy of plus or minus 5 per cent. The highly successful development of the hydrogen sulphide detector tube suggested the possibility of detecting other gases. There quickly followed the development of aphosphide detector tube for quality control of acetylene production, and an ammonia detector tube for quality control of ammonium sulphide production. In this way the Kitagawa gas detector tube was established as a new gas detection method enabling anyone to quickly, and with a high degree of accuracy detect and measure concentrations of gases in different process environments. Kitagawa detectortubes, first used for process and quality control, quickly penetrated into the field of industrial hygiene in the 1950’s when detector tubes were developed for the measurement of chlorine leakage in electrolytic soda plants and for carbon monoxide build-up in coal mines. Today, the Kitagawa Toxic Gas Detector System represents well over 200 different kinds of detector tubes, as part of a completesampling and analysis system to detect and measure toxic gases and materials. Each production lot of tubes undergoes strict quality control and testing to ensure their performance.
1.2 GAS DETECTOR TUBE METHOD 1.2.1 PRINCIPLE
Kitagawa gas detector tubes are made from high-quality borosilicate glass tubes with a uniform inside diameter. Inside, each tube is packed with a gas detectingreagent.When both ends of a detector tube are broken, inserted into the Model AP-20 Kitagawa Gas Aspirating Pump, and an air sample is pulled through the tube by means of pulling back on the pump handle, the detecting reagent changes colour. The length of the discoloured layer is proportional to the concentration of the gas or vapour in the sample because of the fixed volume of sample, which is always 100ml. The relationship between the length of the discoloured layer and the concentration of gas is shown in FIG. 1.1. Graduations printed on the tube showing the gas concentration make it fast and easy to take a reading with Kitagawa detector tubes.
50 40 Discoloured Length 30 20 10 20 300m R mm Sample amount mm
50 40 Discoloured Length 30 20 10
20 100m R