Gas leak

The gas pressure in the first hexapole section is influenced by gas leaking in from the inlet system and, at about 10" mbar, is higher than desirable if excessive ion/neutral collisions are to be prevented. Therefore, the first hexapole is separated from the second hexapole section by a small orifice, which allows ions to pass through. 

The physical properties of the principal constituents of natural gas are Hsted in Table 5. These gases are odorless, but for safety reasons, natural gas is odorized before distribution to provide a distinct odor to warn users of possible gas leaks in equipment. Sulfur-containing compounds such as organic mercaptans, aUphatic sulfides, and cycHc sulfur compounds are effective odorants at low concentrations and are added to natural gas at levels ranging from 4 to 24mg/m. ... 

Cross-country gas pipelines generally must odorize the normally odorless, colorless, and tasteless gas ia urban and suburban areas, as is required of gas distribution companies. Organosulfur compounds, such as mercaptans, are usually used for this purpose, and code requires that the odor must be strong enough for someone with a normal sense of smell to detect a gas leak iato air at one-fifth the lower explosive limit of gas—air mixtures. The latter is about 5%, so the odorant concentration should be about 1%, but most companies odorize more heavily than this as a safety precaution. 

Efficiency for a turboexpander is calculated on the basis of isentropic rather than polytropic expansion even though its efficiency is not 100 percent. This is done because the losses are largely introduced at the discharge of the machine in the form of seal leakages and disk friction which heats the gas leaking past the seals and in exducer losses. (The exducer acts to convert the axial-velocity energy from the rotor to pressure energy.)... 

The turboexpander dry gas seal consists of the conventional dry gas seal mating ring and primary ring, an outboard labyrinth, an inboard labyrinth, and tlie cavity to be vented, if desired. Tlie outboard labyrinth reduces warm seal gas leakage to the process side efficiency deterioration is thus minimized. The inboard labyrinth, on one hand, provides an additional seal between the process and lubricating fluids. On the other hand, it allows injection of an inert gas, if desired. In the latter case, inert gas leaks to the bearing side and to the cavity between the... 

The double opposed seal is used in applications where a zero process leakage is mandated. The seal consists of two seal faces, with the process side seal reversed. An inert gas is injected between the two seals at a positive differential over the process gas pressure. A small amount of the inert gas leaks into the process. The process must be able to accept the contamination of the buffer gas for this seal to be used. 

If a gas leak test is called for, the test can take place shortly after the hydrotest, especially on the reciprocator cylinder or centrifugal or rotary compressors, where the gas is tested without end seals. 

CLASS c FIRE A firc involving gases or liquefied gases in the form of a liquid spillage, or a liquid or gas leak. 

HYDROCARBONS Organic compounds that contain only hydrogen and carbon. The major sources of hydrocarbons in the atmosphere are vehicle emissions (unburned fuel) and gas leaks. Contributes to acid rain. 

Dry powders are effeetive on flammable liquid or eleetrieal fires. Speeial powders are available for use on metals. Dry powder extinguishers may be used on Class C fires, ineluding gases and liquefied gases in the form of a liquid spillage or a liquid or gas leak. This must be aeeompanied by other aetions, e.g. stopping the leak this is neeessary to avoid aeeumulation of an unburned flammable gas-air mixture whieh eould subsequently result in an explosion. Aetivation may be automatie by a deteetion system, or manual. 

Arrangement to deal with reports of gas leaks and suspected CO emissions. 

Provide an emergency response plan for flammable gas leaks in ihc. 

Fuel cannot be completely eliminated, though the inventory of combustible fuels can be kept to a minimum. Oil and gas will be present in any production facility, and either an oil spill or escaping gas can provide the fuel needed. Escaping gas can result from rupture, opening a closed system, or gas that is normally vented. The amount of fuel present can be minimized by preventing oil spills and gas leaks. 

In addition, they are usually constructed without isolation valves on the fuel supply lines. As a result the final connection in the pipework cannot be leak-tested. In practice, it is tested as far as possible at the manufacturer s works but often not leak-tested on-site. Reference 32 reviews the fuel leaks that have occurred, including a major explosion at a CCGT plant in England in 1996 due to the explosion of a leak of naphtha from a pipe joint. One man was seriously injured, and a 600-m chamber was lifted off its foundations. The reference also reviews the precautions that should be taken. They include. selecting a site where noise reduction is not required or can be achieved w ithout enclosure. If enclosure is essential, then a high ventilation rate is needed it is often designed to keep the turbine cool and is far too low to disperse gas leaks. Care must be taken to avoid stagnant pockets. 

Liquefied gas leaked into a steam line that had been blown down. Ice then formed on the outside of the steam line. 

A boiler had been shut down for the repair of a forced draft fan. A blind was not installed in the fuel gas line, nor apparently was a double block and bleed in the fuel line utilized. Gas leaked into the firebox during the repair period and was not removed. A severe explosion occurred during the attempt to light of. 

Figure 4.4 gives an example of an OAET for events that might follow release of gas from a furnace. In this example a gas leak is the initiating event and an explosion is the final hazard. Each task in the sequence is represented by a node in the tree structure. The possible outcomes of the task are depicted as "success" or "failure" paths leading out of the node. This method of task representation does not consider how alternative actions (errors of commission) could give rise to other critical situations. To overcome such problems, separate OAETs must be constructed to model each particular error of commission. 

FIGURE 4.4. Event Tree for a Gas Leak from a Furnace (S=Success F=Failure). 

Task Analysis and Error Analysis of the Blowdown Operation Task analysis was carried out in order to organize all the performance data about the way that workers process information, the nature of the emergency and the way that decisions are made. Figure 7.20 shows a tabular task analysis of the workers response to a significant unignited gas leak in MSM. The analysis was a combination of a tabular HTA and a CADET analysis (see Chapter 4). Human error analysis identified the major human failure modes which could affect time to blowdown (see Table 7.2). 

CR Yellow Alert Gas leak in MSM Audible alarm, yellow flashing light on fire gas panel Uncertain could be real 1. Accept alarm 2. Cz area technician 3. Make PA announcement 4. Determine which gas detector is in alarm (its location) Suspend current operation. Scan panels for flashing yellow or red light. Turn around to MSM Fire Gas panel. Press "accept" button CCR Layout MSM Fire Gas panel Visual and audible Whatever op is doing when alarm occurs Initially disorientating because MSM does not have its own sound source. Alarm could be missed if second simultaneous alarm occurs on main bank of Fire Gas panels... 

Go to radio. Radio Area Technician (AT) to go to MSM and verify gas leak. Radio channel availability Noise, Interference. AT may be busy. Channels may be unavailable... 

FIGURE 7.20 Task Analysis of Operator Response to a Significant Unignited Gas Leak in MSM. 

As was Uie case in Oppau, Germany, in 1921, everyone with firstliand knowledge of the disaster was killed on the site, leaving tlie cause of the incident unknown. It is reasoned tliat a structural weakness in one of the tanks caused the gas leak, although the liquefied gas was not under any pressure. The tanks were only 3 years old when tlie accident occurred and certainly were not expected to... 

To estimate tlie potential iiupaet on tlie publie or tlie environment of aeeidents of different types, the likely emergeney zone must be studied. For example, a liazardous gas leak, fire, or explosion may eause a toxie cloud to spread over a great distance. The minimum atmospheric dispersion model. Vtirious models can be used tlie more difficult models produce more realistic results, but tlie simpler and faster models may provide adequate data for planning purposes. A more tliorough discussion of atmospheric dispersion is presented in Part 111 - Healtli Risk Assessment. 

Other energy sector concerns are methane emissions from unburned fuel, and from natural gas leaks at various stages of natural gas production, transmission and distribution. The curtailment of venting and flaring stranded gas (remotely located natural gas sources that are not economical to produce liquefied natural gas or methanol), and more efficient use of natural gas have significantly reduced atmospheric release. But growth in natural gas production and consumption may reverse this trend. Methane has... 

Natural gas must always be contained in appropriate pipes or vessels and precautions taken to ensure that leakage cannot occur. If a gas leak does occur, the main gas supply should be shut off, the area ventilated and the gas supplier informed. Electrical switches should not be turned on or off, portable electrical appliances including handheld torches should not be operated and all other possible sources of ignition removed or rendered inoperable and the affected area ventilated. In circumstances of excessive leakage, the building should be evacuated. 

Location is of the greatest importance. It is not known from where a gas leak will emanate and such a leak will disperse rapidly. In general, a high-level location should be chosen, as gas is lighter than air. More than one detector will usually be advisable. 

Two types of ultrasonic systems are available that can be used for predictive maintenance structural and airborne. Both provide fast, accurate diagnosis of abnormal operation and leaks. Airborne ultrasonic detectors can be used in either a scanning or contact mode. As scanners, they are most often used to detect gas pressure leaks. Because these instruments are sensitive only to ultrasound, they are not limited to specific gases as are most other gas leak detectors. In addition, they are often used to locate various forms of vacuum leaks. 

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