Our White Papers

How often has a project in your facility been delayed or endured budget overruns due to a lack of readily available and accurate engineering and safety information? How many times have you updated the same information in a piping and instrumentation diagram (P&ID) and other process safety information (PSI) in successive process hazard analyses (PHAs)?

QRA and ERS Analysis are both components of a successful Process Safety Management Program. While both studies often share the same information, they tend to remain separate, independent, studies. However, at facilities where relief valves can vent toxic and flammable materials directly to the atmosphere, these discharges can be a significant contributor to overall risk.

Explosions can occur in vessels or enclosures containing flammable gases and/or dusts. Explosion venting, often referred to as deflagration venting (because we cannot practically vent detonations), is used to protect from catastrophic vessel/enclosure failure. Simplified equations are often used to determine the deflagration relief requirements. Simplified equations can be found in standards such as NFPA-68 [1]. While easy to use, simplified equations tend to overestimate the relief requirements and have several practical limitations.

Although non-equilibriumflow and rapid phase transitions (RPT) are well researched, the literature published so far does not explicitly quantify the RPT phenomenon or provide reliable methods for the calculation of non-equilibrium flow for mixtures.

The development of accurate chemical interaction matrices can provide valuable information for the management of potential chemical reactivity hazards. SuperChems™ 1, a component of Process Safety Office® 2, provides intuitive and easy to use utilities for the rapid development of chemical interaction matrices. These utilities were developed based on known heuristics and rules for the interaction of certain chemical groupings.

A properly sized reclosing pressure relief valve (PRV) can protect process equipment against a variety of overpressure scenarios. Fire exposure scenarios leading to overpressure are particularly challenging, especially where a reclosing pressure relief device provides the only means of pressure relief.

This paper discusses how RAGAGEP considerations now require evaluation and proper documentation of risk factors that are often overlooked including but not limited to: dispersion analysis, thermal radiation, noise, vibration risk, reaction forces and structural supports, metal cold temperatures due to expansion cooling and two phase flow, hot temperatures due to fire exposure and/or runaway reactions, PRV stability, chemical reaction systems, and loss of high pressure/low pressure interface.

It is a common practice to insulate storage tanks containing reactive chemicals to protect against fire exposure. While this mitigation technique is appropriate for vessels handling non-reactive chemicals, reactive chemicals storage represents a special challenge and must be examined on a case-by-case basis.

The risks of shell and tube heat exchanger (STHE) sudden tube failure scenarios are often considered in relief and flare systems design and evaluation. Scenarios involving the release of high pressure gas following a sudden tube failure, especially where the shell is filled with liquids, require the use of relief and flow dynamics for better understanding of and assessment of risks, risk reduction, and relief requirements.

The landscape of relief systems and general process safety management compliance is evolving. This evolution is due in part to enforcement or potential enforcement of RAGAGEP. Because of RAGAGEP [1, 2] considerations, oversizing a relief device is no longer acceptable or desirable from an engineering perspective and from a legal liability perspective.

Numerous scenarios can lead to retrograde and phase change (RPC) flow in relief and depressuring systems. Potential hazard scenarios considered often include, but are not limited to, depressuring during process upsets (cold depressuring), relief or depressuring under fire exposure, and relief or depressuring under runaway reactions.

Retrograde and phase change (RPC) flow considerations are important for relief and flare systems design and evaluations. RPC flow can occur in high pressure systems, including subcooled and/or supercritical flow, or at lower pressures where the starting relief conditions are close to a phase boundary.

Safe design has long been a priority in the process industries. It is a design that effectively minimizes the likelihood of process hazards and mitigates their potential consequences to achieve tolerable risk.

Risk-ranking is a common methodology for making risk-based decisions without conducting quantitative risk analysis. The basis for risk ranking is the risk matrix that has both a consequence and frequency axis. The product of consequence and frequency provides a measure of risk.

The main purpose of the Consequence Analysis phase to be developed during the execution of a risk-based quantitative assessment is to answer the following question: “Which are the impacts of identified hazardous scenarios?” This step is critical for estimating reliable and accurate effects / consequences from Loss of Containment scenarios (LOCs), avoiding unrealistic results that would directly impact on the decision-making process. Additionally, it is essential that Consequence Analysis includes the identification and quantification of ALL potential outcomes that a hazardous release may cause. Event Tree Analysis (ETA) methodology is a valuable tool for identifying all these potential outcomes. The present paper introduces the consequence analysis step by providing guidance on consequence modeling (i.e., source term characterization, dispersion of harmful gases/vapors, fires and explosions) and criteria for event trees development.