Methods of gas protection

A wide range of gas protection measures is available. The most commonly used methods to protect developments can be divided into groups as follows  

There are also active gas pumping systems that are used in landfill sites to collect landfill gas for re-use or flaring. These are not commonly used on development sites and are not discussed further (sites where gas can be abstracted are usually not suitable for development). 

Current UK construction practice adopts the concept of multiple gas protection measures, that comprise a gas control system, since no one protective measure is immune from factors unknown to or outside the control of tire designer. Typically, protection measures increase in number and robustness with the higher characteristic situations defined in Chapter 6. 

This chapter describes the various methods of protection that are available. Chapter 8 describes how to define the scope of protection for any site or building together with the calculations that are required to complete the detailed design of venting and pressurisation systems. 

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Zhang Ying. 2000. Processing method of gas accumulation in Xinji Mine. Mining Safety Environmental Protection. 27(3) 23-24. 

As a matter of fact, almost all of the above-mentioned materials are used in oil and gas industries, but the most common material that is used in bulk quantities is steel and its various types. The tonnage of other materials used is negligible compared to that of steel. Further, as it is well known that steel, in any form, is prone to corrosion, all steels used need to be protected by one or more methods of corrosion protection coatings, inhibitors, or cathodic protection. 

To model the surface emission rates of a gas or vapour an analysis of the vertical flow of gas in the ground is required. The most commonly used method to estimate surface emission rates is based on the simple assumption that a 50 mm borehole has a radius of influence of 1.78 m which is equivalent to a surface area of 10 m (Pecksen, 1991). This radius of influence was an arbitrary value chosen to ensure that surface emissions were not underestimated. It is important to understand that the area of 10 m applies to the surface area surrounding the borehole at ground level and is an estimate of the area of emission of gas from a single borehole. It should not be confused with the area of influence over the depth of the borehole in which gas is assumed to migrate and enter the headspace. The area of emission and the area of influence are not necessarily the same but are often misinterpreted by designers of gas protection systems. 

The scope of a gas protection system is based on the results of the risk assessment. A combination of measures is usually used to minimise the risks associated with ground gas. This is so that if one element of the protection fails the others will continue to protect the development. Once the scope has been defined, detailed design of individual elements such as the venting or membranes can be completed. The latest QRIA guidance has two methods of defining the scope of gas protection one that is for low-rise housing and a ventilated underfloor void (minimum 150 mm high) the other is for any other type of development. 

The system for low-rise housing was developed for the NHBC and the GSV is used to determine the colour-coded classification of a site and the corresponding scope of protection required. This method assumes that all developments have a ventilated underfloor floor void as the minimum protection for the green classificahon. For all other types of development the scope of gas protection measures is determined by using a modified version of the approach described by Wilson and Card (1999). 

Three types of anodic protection can be distinguished (1) impressed current, (2) formation of local cathodes on the material surface and (3) application of passivating inhibitors. For impressed current methods, the protection potential ranges must be determined by experiment (see information in Section 2.3). Anodic protection with impressed current has many applications. It fails if there is restricted current access (e.g., in wet gas spaces) with a lack of electrolyte and/or in the... 

The New Jersey Department of Environmental Protection uses the TXDS method of consequence analysis to estimate potentially catastrophic quantities of toxic substances, as required by the New Jersey Toxic Catastrophe Prevention Act (TCPA). An acute toxic concentration (ATC) is defined as the concentration of a gas or vapor of a toxic substance that will result in acute health effects in the affected population and 1 fatality out of 20 or less (5% or more) during a 1-hr exposure. ATC values, as proposed by the New Jersey Department of Environmental Protection, are estimated for 103 extraordinarily hazardous substances and are based on the lowest value of one of the following (1) the lowest reported lethal concentration (LCLO) value for animal test data, (2) the median lethal concentration (LC50) value from animal test data multiplied by 0.1, or (3) the IDLH value. 

Extinguishing Methods 6 Stop flow of gas and protect exposures with water spray until flow is stopped. 

Research on water explosion inhibiting systems is providing an avenue of future protection possibilities against vapor cloud explosions. British Gas experimentation on the mitigation of explosions by water sprays, shows that flame speeds of an explosion may be reduced by this method. The British Gas research indicates that small droplet spray systems can act to reduce the rate of flame speed acceleration and therefore the consequential damage that could be produced. Normal water deluge systems appear to produce too large a droplet size to be effective in explosion flame speed retardation and may increase the air turbulence in the areas. 

The use of two separate electrical or mechanical zones of detectors, both of which must be actuated before the confirmation of a fire or gas detection. For example, the detectors in one zone could all be placed on the north side of a protected area, and positioned to view the protected area looking south, while the detectors in the second zone would be located on the south side and positioned to view the northern area. Requiring both zones to be actuated reduces the probability of a false alarm activated by a false alarm source such as welding operations, from either the north or the south outside the protected area. However this method is not effective if the zone facing away from the source, sees the radiation. Another method of cross zoning is to have one set of detectors cover the area to be protected and another set located to face away from the protected area to intercept external sources of nuisance UV. If welding or lighting should occur outside the protected area, activation of the alarm for the protected area would be inhibited by second... 

The prime method of protection from a gas explosion in the enclosure is through gas detection and... 

Gather important information the agent used was it aerosol, liquid, gas, powder or vapor location method of delivery do you have the necessary personal protective equipment (PPE) to deal with the hazard, or have you called for assistance by a specialized team are you sure that anyone who enters a contaminated area has the proper PPE and is trained in its use be sure to establish control — keep all victims, non-victims and bystanders at the crime scene (if there is any suspicion of an attack) until it is determined who among them may be a terrorist or a witness perform decontamination, triage if necessary, isolation, quarantine, search and locate evidence, maintain chain of control, and collect samples. 

Commonly used methods for the determination of petroleum hydrocarbon contamination in soil are modifications of Environmental Protection Agency method 418.1, which use sonication or a Soxhlet apparatus for analyte extraction and either infrared spectrometry [5] or gas chromatography with flame ionization detection [6-7] for extract analysis. Regardless of the analytical method following the extraction, both modifications use Freon-113, which has been implicated as a cause of ozone depletion. Therefore, alternative methods are being sought for the determination of hydrocarbon contamination in environmental samples that reduce the need for this halogenated solvent. 

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