Equipment, Exposure, Emission Review—Specification of Process Equipment for Worker Exposure Control

Abstract

Worker exposure to chemical agents may occur from equipment leaks in closed processes and from open system activities and maintenance (e.g., sampling, tank gauging, line breaking, equipment flushing, and drainage). To prevent worker overexposure to chemical agents, an Equipment, Exposure, Emission Review (EEER) was developed to consistently match equipment properties to the leakage-related inhalation risk posed by each stream. For streams where gas or liquid leakage could cause worker exposure above occupational exposure limits (OEL), the EEER recommended a high performance, low leakage equipment category. Conversely, where standard engineering offered reliable containment for lower health risk streams, the EEER did not recommend over-control. The EEER matched equipment to stream health hazard as follows: (1) the composition of each stream was determined, with particular attention to chemical substances with stringent exposure limits; (2) a mixture exposure limit was calculated for each stream based on stream composition and the OEL for stream constituent chemicals; (3) each stream was classified as to its respiratory exposure hazard on the basis of the stream exposure limit; (4) equipment was recommended as a function of respiratory exposure hazard class using an Equipment Selection Matrix. Equipment options were based, in part, on the emission performance of the equipment and a near-field dispersion model that was used to relate equipment emissions to an OEL. Over a 5-yr implementation period, nearly 1700 streams of 78 refining process units were reviewed. Standard engineering practice was selected for about 70% of the streams reviewed. Benzene, hydrogen sulfide, ethanolamine, and high boiling aromatic oil streams were the primary chemical agents responsible for more stringent controls. Although the EEER criteria for stream classification and control options were arranged in order of magnitude—a form of control banding—the correct selection of control technology was based on detailed assessment of stream composition and risk, rather than on process unit name or function. The EEER and Equipment Selection Matrix provided reproducible recommendations and helped manage cost and complexity of equipment specification for health protection.

Keywords:

• engineering
• industrial hygiene
• refinery

ACKNOWLEDGMENT

Support for this work was provided by the Mutualized Strategic Program of Exxon Mobil Corporation and Affiliates.