Continuous gas-detection system

Provide a continuous gas detection system to detect the presence of gas at or below the permissible exposure limit or ceiling limit in lab areas that stwe and use toxic and highly toxic gases. The detection system shall initiate a local alarm and an alarm in the emergency console in the process control center. The alarm shall be both visible and audible. The system shall be provided with ema-gency power. 

A continuous gas detection system must be provided to detect the presence of hazardous (toxic or highly toxic) gases at or below the permissible exposure limit (PEL) orthe ceiling limit (see UFC 8003.3.1.6). The detection system must initiate a local audible and visual alarm as well as transmit a signal to a constantly attended plant Emergency Control Station (ECS). Activation of the alarm/monitoring system must automatically close the shutoff valve on highly toxic or toxic gas supply lines. 

A continuous gas-detection system is required by Uniform Fire Code Article 51 and Article 80, where toxic or highly toxic gases are stored, dispensed or used. The system must continually monitor use areas for the potential presence of fugitive gases. These systems must be designed in accordance with ... 

Various simple and sophisticated fire and gas detection systems are available to provide early detection and warnings of a hydrocarbon release which supplement process instrumentation and alarms. The overall objective of fire and gas detection systems are to warn of possible impending events that may be threatening to life, property of continued business operations, that are external to the process operation. 

The detection and alarm circuits of fire and gas detection systems should be continuously supervised to determine if the system is operable. Normal mechanisms provide for a limited current flow through the circuits for normal operation. During alarm conditions current flow is increased while during failure modes the current level is nonexistence. By measuring levels at a control point the health of the circuit or monitoring devices can be continuously determined. End-of-line-resistors (EOLR) are commonly provided in each circuit to provide supervisory signal levels to the control location. 

While various codes may differ in definition and/or scope, there is a recurring requirement for continuous gas detection by atoxic gas monitoring system (TGMS). 

The primary purpose of a gas detection system is to continuously monitor an area for the presence of hazardous and toxic gases at or below a specific concentration limit, and if necessary, warn personnel through both visual and audible alarms prior to the onset of a life threatening condition. W... 

Automatic Continuous Air Monitoring System (ACAMS) This system can detect G agents, VX, or mustard agents at very low levels. It is an automatic gas chromatograph that first collects agent on a solid sorbent and then thermally desorbs the agents into a separation column for analysis. 

The system provides a very sensitive means of detection levels of 10 picograms absolute are measurable with the continuous (permanent) trapping system. A further advantage is that the software calculates the analytical results directly in concentration in the unit volume of sample introduced. However, it should he stressed that the level of mercury measured is an absolute quantity and while the detection Hmit is of the order of 10 picograms, this quantity can be contained in any volume of gas. In addition, the fact that the mercury both absorbs and fluoresces to provide a measurement which can be measured with a specific retention time provides more positive evidence of the presence of mercury. 

There are several reasons for this exceptional situation. First, production of transactinides at accelerators implies a thermalization of the primary products in a gas, usually helium. It is rather straightforward to connect such a recoil chamber to a gas chromatographic system. Second, gas phase separation procedures are fast and may be performed in a continuous mode. Third, at the exit of the chromatographic column separated volatile species can be easily condensed as nearly weightless samples on thin foils. This enables detection of a decay and spontaneous fission (SF) of the separated products with supreme energy resolution. 

The nature of the tracer dictates the detection system. For the liquid phase, quite often the tracers (e.g., NaCl, H2S04, etc.) are such that the detection probe is directly inserted into the reactor and continuous monitoring of the concentration at any fixed position is obtained by means of an electrical conductivity cell and a recorder. In this case, no external sampling of liquid is necessary. If the tracer concentration measurement requires an analytical procedure such as titration, etc., sampling of the liquid is required. For the solid phase, a magnetic tracer is sometimes used. The concentration of a solid-phase tracer can also be measured by a capacitance probe if the tracer material has a different dielectric constant than the solid phase. In general, however, for solid and sometimes gas phases, some suitable radioactive tracer is convenient to use. The detection systems for a radioactive tracer (which include scintillation counters, a recorder, etc.) can be expensive. Some of the tracers for the gas, liquid, and solid phases reported in the literature are summarized in Table 3-1. 

In some cases, a given step can be coupled on-line with USAL but off-line development provides better results. Such is the case with a method for the determination of the frans-fatty acid content in bakery products [32] following isolation of total fat, the fatty acids must be derivatized to methyl esters, which are volatile, for subsequent analysis by gas chromatography separation with mass spectrometry as detection system. The derivatization reaction must be complete, selective and sensitive enough, which is difficult to accomplish in a continuous manner as the procedure involves ... 

The response of this detector is based on the fact that the frequency output from piezoelectric material is influenced by the weight of the coatings or layers on its surface. This effect has been used for many years to measure trace concentrations of water vapor in a gas and xylene vapor in air has been detected by this means at concentrations as low as lO g/ml. It was first introduced as a GC detecting system by King [22]. The detector consists of a quartz crystal (coated with a high boiling liquid) that is appropriately situated in an electronic circuit that causes it to oscillate at its natural frequency. The oscillation frequency is continuously monitored by a separate circuit. 

Fire prevention methods are based on proper operation and cleaning of the dryer. An important safety device is an automatic control systan (ACS), as it can maintain the tanpera-ture within 1 C range whereas the manually controlled temperature may vary 10 C. The control system shonld include a detection system of parameter deviation, deposit deteaion, drying gas analysis, and continuous monitoring of the humidity and temperature at selected locations. 

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