Project Profile
Toxic Dispersion Assessment for Roof Mounted Ventilation System
Read how ABS Group helped a major chemical company understand the dust hazard risk for a new piece of equipment installed at the plant.
Project Objectives
#1
Produce a Computational Fluid Dynamics Model to simulate the release on the roof
#2
Monitor the H12MDI levels from kneeling and standing heights
#3
Determine the worst case release and environmental conditions and simulate the dispersion
Project Overview
A major chemical company's roof ventilation system had the potential to vent vapor containing a sub-1-ppm concentration of Hydrogenated MDI into the air. Several individuals were working on the roof at different elevations, making the vapor a cause for concern as it had the potential to impact the health of all personnel working on the rooftop.
Client Needs
- Determine the risk to personnel working on the roof at various elevations
- Comply with OSHA PSM and EPA RMP regulations
Our Solution
ABS Group used Recognized and Generally Accepted Good Engineering Practices (RAGAGEP) developed through years of experience in preparing facility siting and hazard assessments in coherence with the American Petroleum Institute (API) and the Center for Chemical Process Safety (CCPS) guidelines.
The building in question had multiple roof elevations, all accessible to personnel. We used FLACS CFD software to simulate the dispersion in order to capture potential interactions of the plume with roof features. The client indicated that there were eight different relative elevations; in response, ABS Group monitored the H12MDI concentration from kneeling (0 ft) to standing height (~6 ft, 2 m) above each roof elevation.
Because the release location was outside, we also collated monthly average weather conditions for the CFD simulations. These conditions, along with the variable release conditions, were used to identify the worst-case release/weather combination. All dispersions were simulated until the plume reached a steady state condition. Once the worst-case release and environmental conditions were determined, a series of simulations were performed, varying the stack height and wind direction.
Based on the simulation results, the client was presented with two options:
- For all roof elevations, a minimum stack height of >~19 ft would meet the H12MDI concentration target. (Inclusion of a safety factor could increase conservatism.)
- For all roof elevations (excluding one specific elevation), a minimum stack height of >~6 ft would meet the H12MDI concentration target. (Inclusion of a safety factor could increase conservatism.)
Value Delivered
We assisted the client in making an informed decision to keep their staff safe from potential toxic substance releases. Our expertise in industry regulation allowed us to help the client meet the requirements and guidelines set by the CCPS and API.