What is a Facility Siting Study?
A Guide to Compliance with OSHA 29 CFR 1910.119
Industrial operations often involve managing hazardous substances such as flammable, explosive, and toxic materials. Proper facility layout and structure placement are key to minimizing safety risks. A Facility Siting Study (FSS) evaluates potential dangers, ensuring the protection of buildings, portable structures, and surrounding areas from concerns such as overpressure, fire radiation, and toxic exposure.
After the BP Texas City explosion, regulatory agencies emphasized the importance of FSS as part of Process Safety Management (PSM). As a result, OSHA 29 CFR Part 1910.119, under 1910.119(e)(3)(v), requires facilities to perform these assessments every five years to identify threats that may affect personnel and infrastructure.
This blog is the first in a two-part series on Facility Siting Studies. We will explore the FSS process, industry guidelines, and hazard consequence analysis. For more details on structural responses during hazardous events, read our second blog: Structural Response in Facility Siting Studies – Evaluating Building Resilience.
In this blog, we will cover:
- Introduction to Facility Siting Studies
- Industry Guidelines and Compliance
- Steps in Conducting a Facility Siting Study
- Consequence-Based Facility Siting Study
- Case Study: CFD vs. Empirical Models
- Risk-Based Facility Siting Study
- Key Takeaways
A Facility Siting Study (FSS) assesses how a facility’s layout affects the impact of various conditions, including:
- Overpressure from explosions
- Thermal radiation from fires
- Toxic gas dispersion
The primary goal is to assess whether existing infrastructure can withstand these events and whether occupants are protected during an incident.
OSHA mandates periodic FSS reviews to reduce accidents and safeguard workers. Using data-driven models, an FSS simulates worst-case and realistic scenarios to help facilities refine risk management practices
Industry Guidelines and Compliance
Facility Siting Studies adhere to industry standards, with key references being:
- API 752: Addresses permanent buildings exposed to process hazards.
- API 753: Examines risks for portable buildings and temporary shelters.
- API 756: Addresses process plants tents.
These standards define acceptable levels and methodologies for evaluating factors such as blast loads, heat radiation, and toxic gas dispersion. The findings help determine whether structures require reinforcement or relocation to maintain operational safety and minimize potential operational disruptions.
Steps in Conducting a Facility Siting Study
A Facility Siting Study involves a structured process to recognize, analyze, and mitigate risks. The key steps include:
1. Scenario Identification
- Methodologies, involve, reviewing plot plans and Piping & Instrumentation Diagrams (P&ID), HAZOP and HAZID findings to locate areas of concern.
- Pinpointing sources of releases (flammable, toxic, or reactive materials).
2. Consequence Analysis
- Exploring the effects of explosions, fire radiation, and toxic gas dispersion using modeling tools.
3. Structural Assessment
- Determining whether buildings can withstand overpressure, fire, or toxic exposure.
- Recognizing the need for retrofits or relocations based on the analysis.
4. API Criteria Assessment
- Checking whether the facility meets API criteria for structural integrity.
- If the criteria are met, the study proceeds to the final report.
- If not, a Quantitative Risk Assessment (QRA) is conducted to refine the analysis.
5. Quantitative Risk Assessment (QRA)
- Perform a detailed analysis to assess the likelihood and impact of various scenarios.
- The QRA helps indicate if the facility needs additional safety measures.
6. Final Structural Assessment
- Reassess the facility’s structure after QRA is completed, to evaluate any changes in risk exposure and determine whether structural modifications are required.
7. API Criteria Reassessment
- After the QRA is performed, check if the facility meets API criteria again.
- If not, proceed to Building Retrofit.
8. Building Retrofit
- Implement structural modifications or reinforcements to address deficiencies and meet necessary standards before finalizing the report.
9. Final Report
- After retrofitting or if the criteria are initially met, generate the final report summarizing findings and mitigation strategies.
Consequence-Based Facility Siting Study
A consequence-based FSS evaluates potential risks by identifying hazards, modeling their impact, and running simulations. Key steps include:
1. Hazard Identification
- Identify potential hazards (chemical releases, fires, explosions, toxic gas dispersion) and their behavior during an incident.
2. Consequence Analysis
- Model the impact of hazards, including blast overpressure, thermal radiation, and toxic gas dispersion, to define affected areas and severity.
3. Identification of CFD Scenarios
- Select scenarios where Computational Fluid Dynamics (CFD) modeling is necessary to predict complex conditions accurately.
4. CFD Run (Key Scenarios)
- Run CFD simulations to model the behavior of events in realistic environments, factoring in variables like terrain, wind, and obstacles.
5. Evaluation of Effective Mitigation
- After CFD simulations, assess whether the proposed mitigation strategies (reinforcements, barriers, emergency plans) reduce impacts. If not, further adjustments are made.
Common Modeling Approaches:
- Leak Size Assessment – Investigating multiple failure scenarios (e.g., 0.5″, 2″, 6″ openings).
- Radiation Modeling – Analyzing fire hazards with 4 kW/m², 12.5 kW/m² thresholds.
- Toxic Dispersion Modeling – Applying ERPG, Probit analysis, and dispersion models.
- Overpressure Analysis – Examining blast impacts at pressure levels such as 0.6 psi and 0.9 psi.
Case Study: CFD vs. Empirical Models
A comparison of empirical models and CFD simulations revealed:
- Empirical models tend to overestimate risks, leading to overly cautious safety measures.
- CFD-based assessments offer more precise, real-world representations of hazard exposure, allowing for more efficient safety strategies.
Important differences between Empirical and CFD-based methods include:
By integrating CFD into facility siting studies, businesses gain a more precise understanding of actual risk exposure and can develop targeted mitigation strategies.
Risk-Based Facility Siting Study: Integrating Frequency and Ignition Probabilities
A Risk-Based Facility Siting Study incorporates event likelihood and ignition probabilities, allowing for more accurate assessments. Key steps include:
1. Hazard Identification
- Find potential concerns based on materials and their behavior during incidents.
2. Consequence Analysis
- Model the potential severity of outcomes, including blast overpressure, thermal radiation, and gas dispersion.
3. Identification of CFD Scenarios
- Select key scenarios where CFD modeling is needed for accurate hazard prediction.
4. CFD Run (Key Scenarios)
- Conduct CFD simulations to model hazard events in real-world conditions.
5. Evaluation of Effective Mitigation
- After CFD simulations, assess whether the proposed mitigation strategies (reinforcements, barriers, emergency plans) reduce impacts. If not, further adjustments are made.
6. Quantitative Risk Analysis (QRA)
- If mitigation is insufficient, conduct a QRA to assess the probability and severity of various hazards and determine necessary safety actions.
Key Takeaways
- Facility siting studies analyze overpressure, fire, and toxic gas exposure using data-driven models.
- Industry standards such as API 752, API 753, and API 756 offer guidelines for identifying site-specific concerns.
- Combining consequence-based and risk-based reviews provides a thorough understanding of risks.
- CFD modeling improves accuracy by delivering detailed insights into exposure and minimizing unnecessary safety margins.
- Regular FSS inspections refine risk-reduction strategies and enhance emergency planning, helping facilities manage operations efficiently.
A well-conducted Facility Siting Study supports risk management and compliance with regulatory standards. It helps prevent incidents and refines facility planning by integrating both consequence-based and risk-based approaches, enabling data-driven decisions to improve safety protocols and meet regulatory requirements.
For a closer look at how buildings respond during hazardous events, read our next blog on Structural Response in Facility Siting Studies.
