Detectors combustible gas

Combustible Gas Concentration Combustible Gas Detector Analyzer Safety High 0 ... 

Combustible gas detection systems are frequently used in areas of poor ventilation. By the early detection of combustible gas releases before ignitible concentration levels occur, corrective procedures such as shutting down equipment, deactivating electrical circuits and activating ventilation fans can be implemented prior to fire or explosion. Combustible gas detectors are also used to substantiate adequate ventilation. Most combustible gas detection systems, although responsive to a wide range of combustible gases and vapors, are normally calibrated specifically to indicate concentrations of methane since most natural gas is comprised primarily of methane. 

Required locations of gas detectors (sensors) are often specified by the authority having jurisdiction. For example, API RP 14C recommends certain locations for combustible detectors. These recommendations have been legislated into requirements in U.S. Federal waters by the Minerals Management Service. RP 14C should be referred to for specific details, but, basically, combustible gas detectors are required offshore in all inadequately ventilated, classified, enclosed areas. The installation of sensors in nonenclosed areas is seldom either required or necessary. Ignitible or high toxic levels of gas seldom accumulate and remain for significant periods of time in such locations. 

Most combustible gas detector sensors are installed in the upper portions of buildings for the detection of natural gas. However, in many cases the vapor which flashes off oil in storage tanks can be heavier than air. Below grade areas should be considered for sensor installations where heavier-than-air vapors might collect. 

It is usual to test for the presence of flammable gas or vapor with a combustible gas detector before maintenance, especially welding or other hot work, is allowed to start. The following incidents show what can happen if these tests are not carried out or not earned out thoroughly. Large pieces of equipment or those of complex shape should be tested in several places, using detector heads at the ends of long leads if necessary (see Section 5.4.2 d). 

The tank had contained a light naphtha and had not been thoroughly cleaned before repairs started. It had been filled with water and then emptied, but some naphtha remained in various nooks and crannies. (It might, for example, have gotten into the hollow roof supports through pinholes or cracks and then drained out when the tank was emptied.) No tests were carried out with combustible gas detectors. 

No one realized, when a site for the furnace was decided, that flammable vapors could come out of the cooling tower. Direct contact condensers are not common, but flammable vapors can appear in many cooling towers if there are leaks on water-cooled heat exchangers. After the incident, a combustible gas detector was mounted permanently between the furnace and the tower (Figure 2-8). 

It is possible to measure the extent of a leak of flammable gas or vapor with a combustible gas detector. If the leak is small, a person may be allowed (but not expected) to put his hands, suitably protected, inside the flammable cloud. But only in the most exceptional circumstances should a person be allowed to put more of his body into the cloud. 

On many occasions combustible gas detectors have detected a leak soon after it started, and action to control it has been taken promptly. Installation of these detectors is strongly recommended whenever liquefied flammable gases or other flashing liquids are handled or when experience shows there is a significant chance of a leak [3]. Detectors are also... 

Install combustible gas detectors to provide early warning of a leak. 

The leak could have been stopped as soon as it was detected if an emergency isolation valve (Section 7.2.1) had been fitted in the pump suction line. On the rebuilt plant such valves were fitted on the pump suction lines, more combustible gas detectors and more extensive insulation were installed, plastic pump bodies were replaced by metal ones, and spillages were directed to collection pits. The plant was built in 1972, when these features were not common practice many improvements had been made since then, but they did not go far enough. Most of those made after the fire could have been made beforehand. 

The process area has combustible gas detectors, fireproofing, and a water deluge system. Cable trays are protected with deluge, and portable dry chemical extinguishers are in the process area. Diesel-powered fire water pumps can provide a maximum fire water demand for 4 hr. 

Loss control features include combustible gas detectors installed around the containment area and transfer system. A diesel-driven fire pump is capable of handling the emergency demand for 4 hr. A water deluge system has been installed around the storage tank and transfer pump. 

Methane leaks from a tank in a 50 m3 sealed room. Its concentration is found to be 30 % by volume, as recorded by a combustible gas detector. The watchman runs to open the door of the room. The lighter mixture of the room gases flows out to the door at a steady rate of 50 g/s. The flammable limits are 5 and 15 % by volume for the methane in air. Assume a constant temperature at 25 °C and well-mixed conditions in the room. The mixture of the room gases can be approximated at a constant molecular weight and density of 25 g/mol and 1.05 kg/m3 respectively. After the door is opened, when will the mixture in the room become flammable ... 

To assist in the location of combustible gas detectors and fire detection equipment. 

Since detectors are by definition exposed to combustible gases they should be rated for electrically classified areas, such as Class I, Division I or 2, the specific gas groups (normally groups C and D), and temperature ratings. It should be noted the UL presently does not specifically test combustible gas detector sensor heads for use in classified areas, although they do tests enclosures for control and data acquisition circuits. Several other international standards do evaluate combustible gas detectors for use in classified areas (e.g., BS 6020). 

American Petroleum Institute (API), API Publication 2031. Combustible Gas Detector Systems and Environmental and Operational Factors Influencing Their Performance. First Edition, API Washington D.C., 1991. 

Instrument Society of America (ISA), ISA-S12.13. Part I-Performance Requirements. Combustible Gas Detectors. ISA, Research Triangle Park, NC, 1986. 

Point Combustible Gas Detectors (IR) are used to indicate the presence of gas at a particular location (e.g., in a congested area of the planter in small ducts.) IR technology has proven to be more reliable than catalytic bead detectors. The point detector functions in the same manner as the open path detector, by comparing absorbed and reference frequencies of IR light. The main difference between these and open path type is that the path length of the point type is short (3 inches) and is kept within the confines of the instrument. 

Combustible gas detectors—where a flammable vapor or gas hazard exists, gas detectors are typically installed. Gas detectors should be arranged to a low set point to sound an alarm and the upper set point to activate the water spray or deluge system. 

Methane in aqueous sample determined by direct readout combustible gas detector, available commercially. 

The most common type of combustible gas detectors utilizes the catalytic combustion principle. A platinum wire filament (in a Wheatstone bridge cir-... 

Before designing enclosures for processes involving flammables, the consequences of poor ventilation that could concentrate the release above the lower flammable limit should be considered. Even if there are no ignition sources, continuously monitored combustible gas detectors should be placed in the enclosure. If all other sources of containment for flammables are inappropriate and enclosures are the only option, a means for extraordinary ventilation of even the smallest release should be provided. In addition, NFPA 68 (1994), Guide for Venting of Deflagrations, should be consulted... 

The amount of thermal radiation (heat) emitted from a hydrogen flame is low and is hard to detect by feeling (low emissivity). Most commercially available combustible gas detectors can be calibrated for hydrogen detection. Typically alarms from these sensors are set by the manufacturer between 10%-50% of the lower flammability limit (TFT) of hydrogen to avoid the presence of an unwanted flammable envi ronment. 

Combustible gas detectors Warning occurs before the fire starts Require more than one instrument to confirm a release Outdoors or indoors. Can be portable... 

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