API PUBL 332-1995

$28.60

Comparison of Screening Values from Selected Hydrocarbon Screening Instruments

Published By	Publication Date	Number of Pages
API	1995	121

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Description

Fugitive emissions from leaking equipment are being monitored by refineries, chemical plants, petroleum marketing terminals and oil and gas production operations. Different instruments, each capable of measuring the fugitive hydrocarbon emissions, or screening values, are being utilized by different studies. The measurement distance to hold the screening instrument from the point of maximum leak also differs for different facilities.

This study evaluated the differences in screening values for the following four different screening instruments:

Foxboro Organic Vapor Analyzer (OVA) 108;

Bacharach Threshold Limit Value Sniffer (TLV Sniffer®)

HNU®PI-101; and

Foxboro Total Vapor Analyzer (TVA) 1000, both flame ionization detector (FID) and photo ionization detector (PID).

This study showed that there were differences in screening values for a particular component based on using the different screening instruments. Adjustment factors, or correlation equations, were developed to allow screening values from the TLV Sniffer®, and the TVA FID to be converted to comparable OVA screening values. Adjustment factors were not developed relating HNU® or TVA PID screening values to OVA screening values because inadequate correlations were found between these screening values.

This study also evaluated the differences in screening values for these screening instruments based on screening as close as possible to the surface of a component at the point of maximum leak versus screening 1 cm away from the component at the point of maximum leak. This study showed that there are differences in screening values if the screening instrument is held at 1 cm away compared to holding the instrument as close as possible to the surface. An adjustment factor, or correlation equation, was developed to convert screening values from the OVA screening instrument using a 1 cm spacer basis to an "at the surface" basis.

Please note that other screening instruments, not studied in this report, maybe available.

A 1979 study on screening distance effects and screening instrument effects was compared to the results of this study. Both studies show comparable differences between the OVA and TLV Sniffer® screening values; however, the screening distance differences were more pronounced in the 1979 study than in this study. The reason for the differences in screening distance results is unknown, These differences could be due to screening techniques, in ambient conditions, or in differences in instrument sensitivities.

An analysis was performed to determine other factors that may affect the relationship between screening values. Insignificant, or minimally significant effects were observed for wind speed, component type and service type.

Additional information