Threshold limit valve

ACGIH. 1986. Documentation of the threshold limit valves and biological exposure indices. 5th ed. American Conference of Governmental Industrial Hygienists, Cincinnati, OH, 296. 

PR valves in toxic vapor services where discharge to the atmosphere would result in the calculated concentration at the property line or at any working area (either at grade or an elevated platform) exceeding the Threshold Limit Value (TLV). 

Commonly reported near misses include such events as exceeding operating limits, a release of a chemical or other hazardous substance that does not meet the threshold for a process safety incident metric, activation of relief valves, interlocks, or ruptured disks. Companies may establish near-miss metrics based on the specifics of their operation, based on their observations of frequent upsets or failures, or to track and correct observed unsafe practices or behaviors. 

Capillary burst valves, which are rotationaUy actuated, stop flow by the counterpressure induced at a capillary feature such as a hydrophobic constriction or a sudden expansion in a (hydrophilic) channel (Fig. 4). If the substrate material is hydrophobic, the valve is typically formed by a constriction in the microchannel. These burst valves yield once the spin rate passed a certain threshold governed by the valve geometry, its radial position, the contact angle, and the surface tension of the liquid. Mainly due to minimum feature sizes and manufacturing tolerances, there is a practical limit which, on the one hand, restricts the maximum burst frequency and, on the other hand, smears out the definition of the nominally discrete burst frequencies into bands. In many applications the number of independently controllable burst valves and thus the number and vigorousness of LUOs are significantly capped [4]. 

Reliable quantitative analysis can be conducted for analytes with concentrations falling within a certain range. Low abundance analytes may not be detected, or their signals would be too low to provide repeatable data for quantitative analysis (if they are below the limit-of-quantification threshold). On the other hand, high abundance analytes may not be quantified reliably because of saturation of the detection system. Therefore, sample dilution is often required. This kind of basic sample preparation (by dilution) can readily be implemented using valves and pumps. However, it may also decrease the temporal resolutions of the real-time monitoring routines. 

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