API RP 77-2018 pdf download.Risk-based Approach for Managing Hydrocarbon Vapor Exposure during Tank Gauging, Sampling, and Maintenance of Onshore Production Facilities.
1 Scope The scope of this standard covers recommended risk assessment and risk management practices to reduce the potential for acute worker hydrocarbon exposures and related atmospheric risks (i.e. potential oxygen deficiency). Specifically, this recommended practice is limited to onshore production tanks (including flowback tanks) during gauging and sampling, open-top tank sampling, and select tank maintenance activities involving removal or opening of tank appurtenances. While the tools and practices recommended in this document can be useful in other operations, this recommended practice does not specifically apply to downstream, refining, or offshore tank applications. This standard specifically excludes risk assessment and management practices related to a) chronic hydrocarbon exposures, b) non-hydrocarbon substances such as hydrogen sulfide, and c) opening other process equipment, confined space entry, tank cleaning, or decommissioning activities. 2 Terms and Definitions For the purposes of this document, the following terms and definitions apply. 2.1 communication protocols A system of rules which allow for two or more entities of a communications system to transmit information. 2.2 flashing losses The release of entrained gas from a liquid as the pressure on the liquid drops. 2.3 gas-to-oil ratio The ratio of the gas produced in standard cubic feet to one barrel of oil produced during any stated period. 2.4 hazard A situation, inherent chemical or physical property with the potential to do harm. EXAMPLE Flammability, oxygen deficiency, toxicity, corrosivity, stored electrical, chemical or mechanical energy. 2.5 hydrocarbon HC Class of organic chemical compounds composed only of the elements carbon (C) and hydrogen (H). NOTE The carbon atoms join together to form the framework of the compound, and the hydrogen atoms attach to them in many different configurations.
2.6 risk A measure of potential injury, environmental damage, or economic loss in terms of both the incident likelihood and the severity of the loss or injury. 2.7 risk assessment The identification and analysis, either qualitative or quantitative, of the likelihood and outcome of specific hazard exposure events or scenarios with judgements of probability and consequences. 2.8 stop work authority A program designed to provide employees and contract workers with the responsibility and obligation to stop work when a perceived unsafe condition or behavior can result in an unwanted event. 2.9 thief hatch A closable aperture in a tank or vessel which are used to take samples of the tanks contents, determining the level of the tank and protect the tank from over pressure and excessive vacuum. 2.10 volatile organic compounds VOCs A chemical class of hydrocarbons that participates in atmospheric photochemical reactions, which have an initial boiling point less than or equal to 250 °C (482 °F) measured at standard atmospheric pressure of 101.3 kPa (14.7 psi). EXAMPLE Methane, ethane, acetone, acrolein, benzene, carbon disulfide, carbon tetrachloride, chlorobenzene, chloroethane, dichlorobenzenes, dichloropropenes, ethylbenzene, formaldehyde, gasoline, hexachlorobutadiene, n-hexane, styrene, tetrachloroethylene (PERC), toluene, trichloroethylene (TCE), vinyl chloride, and xylenes, to name a few. 3 Hazard Identification 3.1 General Hazard identification begins with understanding the source of the natural gas and the processes that can potentially contribute to concentrations of tank vapors. Successful and safe tank management begins with an understanding of the production fluid characteristics, and the influence of process design, operations, and maintenance considerations that can impact risk. 3.2 Fluid Characteristics Understanding the physical properties of produced VOCs, including hydrocarbons, is essential in identifying potential hazards. Tank contents, including volatile hydrocarbons
3.3 Process Design, Operational, and Maintenance Considerations Process design and operational factors are also essential to understanding potential exposure hazards as they can impact vapor volume and concentrations. Hazard identification approaches should include characterization of process and operational factors (see Annex A checklists). Key factors include, but are not limited to, the following: a) equipment sizing relative to anticipated production flow rates; b) liquids retention time; c) pressure and flow control impacts on separation; d) presence or absence of chokes and choke points; e) back pressure and pressure relief systems, which may include blanket gas systems, flare systems, etc.; f) ability to isolate tanks; g) ability to isolate vent lines; h) environmental factors including geographic location, temperature, wind speed, altitude, etc.; i) maintenance and operating procedures; j) maintenance and reliability of process equipment that can influence pressure balance (e.g. pressure relief valves, flare knockout pots, flare flame arrestors, etc.); k) emissions controls present.