Facility Siting for a Chemical Manufacturer Case Study

The Challenge

A U.S. chemical company planned to install a new carboxylic acid manufacturing unit at one of its facilities, allowing nitric acid (HNO3) to be recovered from its manufacturing process via absorption recovery and thermal oxidation. To ensure that the new manufacturing unit was operated and maintained in a safe manner, a facility siting study was required. This would ensure that adequate spacing and other considerations were incorporated into the unit design. The study would need to take into account the spacing of new equipment as well as the spacing to surrounding process units and buildings. Concerns about occupant safety also needed to be addressed.

Our Approach

The ioMosaic team employs a three-pronged approach when performing facility siting studies (a) to identify the buildings at risk, (b) assess if the risk is tolerable, and (c) recommend cost-effective risk reduction where applicable to as low as reasonably practicable (ALARP). For this facility siting, both a hazard identification and consequence assessment were conducted during the consequence-based approach and risk-based approach. Additionally, frequency analysis and risk assessment were completed during the risk-based approach to estimate the risk levels of the new manufacturing unit.

ioMosaic software Process Safety Office^® SuperChems™ features a database with the capability to locate buildings and other critical infrastructure on an actual site map and then define infrastructure information, such as occupancy levels for different types of populations, construction types, and so on. The site map catalogs the overpressure time histories and the structural response of each building. The source term and explosion dynamics models are very detailed and well-validated.

Consequence-Based Approach

The first step determined whether the occupied buildings were impacted by toxicity, thermal radiation, or overpressure. Based on the consequences of the scenario, the hazard contours were established and the building risk was assessed.

Risk-Based Approach

In the risk-based method, also referred to as the Quantitative Risk Analysis (QRA) method, all scenarios leading to loss of containment were first identified. A frequency of occurrence was then established for each scenario. Risk contours were established for the entire facility. These contours were then used to identify buildings and other infrastructure at risk. For facility siting study, risk contours are typically established for specific overpressure levels. For example, a structure of typical construction (not blast proof) falling within the 3 psi contours at a frequency of 1/10,000 years or more would be considered at risk. Maximum Individual Risk (MIR) and Aggregate Risk (AR) were the two main types of risks assessed.

Equipment Spacing Analysis

The final stage involved comparing the projected site layout to industry-recommended process unit and offsite layout guides.

The Benefits

The client now had a documented systematic equipment-by-equipment analysis of the planned occupied buildings, any potential hazards identified, and the likelihood of their occurrence. The facility siting study showed that the new manufacturing unit design met industry compliance safety standards.

Using the consequence-based approach, we determined that the planned locations of the new manufacturing unit design were acceptable for thermal radiation due to jet fires. Using the risk-based approach, we determined that the planned locations of the new manufacturing unit design were acceptable for toxicity from toxic dispersions, overpressure from vessel bursts, and vapor cloud explosions. Because both the individual and societal risks were tolerable, it was not necessary to identify further means of risk reduction.

Based on the results of the equipment spacing analysis, most of the equipment distances between the analyzed equipment were within acceptable limits. In some cases, the measured distances between equipment were less than the recommended distances but because the risk was tolerable, these distances were also deemed acceptable.

Learn More

Our mission is to help you protect your people, your plant, your stakeholder value and our planet. To learn more about how we can help you manage risk, call us at 1.844.ioMosaic.