METHODOLOGY FOR VENT DISPERSION ANALYSIS STUDY

METHODOLOGYMETHODOLOGY FOR VENT DISPERSION ANALYSIS STUDY
08/12/2023	1	Final	AM	SS	YSG
Date	Rev	Remarks / Revision Summary	Prepared	Checked	Approved
			HSE RMSPL
REVISION RECORDS

DISCLAIMER

This methodology has been prepared on behalf of and for the exclusive use of M/s XXXXX and is subject to and issued in accordance with the contract between M/s XXXXX and HSE Risk Management Services Private Limited. HSE Risk Management Services Private Limited accepts no liability or responsibility whatsoever for it in respect of any use of or reliance upon this Methodology by any third party.

Copying this Methodology without the permission of M/s XXXXX or HSE Risk Management Services Private Limited is not permitted.

Proposed Methodology

• Introduction
• Vent is used for safe disposal of the vented gases to the atmosphere. Flammable or toxic gases are released from the vent. To ensure that the hazards of venting these gases are tolerable for the people near the site, a quantitative hazard analysis of gas venting is often required. 
• The Dispersion study is carried to estimate and identify the quantity of material release from the vents to atmosphere, potential hazards and its effects, occurrence of hazards during the process.
• Gas dispersion is typically performed using specialized software such as PHAST/ Safeti which is in-built with complex dispersion and transport phenomena equation and Unified dispersion model (UDM) to assess all phases of the dispersion.
• Some of the common key inputs are Vent orientation, Properties of the vented fluid like flow rate, duration of release, composition, pressure, temperature , Surrounding area , Weather / wind conditions etc.

• Methodology

Dispersion study methodology involves a series of steps as follows:

• Identification of release points (atmospheric vents/ flare stack)
• Gathering of inputs required for initiating the study by reviewing project documents such as project scope definition, P&ID, PFD and Heat & Material Balance sheets
• Source term definition and collection of process data of identified release points
• Study of meteorological input data and selection of wind speed & stability class.
• Source term modeling and consequence analysis using PHAST/ SAFETI software for the identified release points
• Extraction of consequence results
• Results analysis, study key findings & conclusions
• Reporting & documentation

1. Introduction to study2. Study Scope of Work3. Review of Project data(Design basis, P&ID, PFA, H&MB, etc.)4. Study Assumption Register5. Source term definition & Modelling using PHAST Tool6. Determination of distance to concentration results for the identified7 Findings & Conclusions1. Introduction to study2. Study Scope of Work3. Review of Project data(Design basis, P&ID, PFA, H&MB, etc.)4. Study Assumption Register5. Source term definition & Modelling using PHAST Tool6. Determination of distance to concentration results for the identified7 Findings & Conclusions1. Introduction to study2. Study Scope of Work3. Review of Project data(Design basis, P&ID, PFA, H&MB, etc.)4. Study Assumption Register5. Source term definition & Modelling using PHAST Tool6. Determination of distance to concentration results for the identified7 Findings & Conclusions1. Introduction to study2. Study Scope of Work3. Review of Project data(Design basis, P&ID, PFA, H&MB, etc.)4. Study Assumption Register5. Source term definition & Modelling using PHAST Tool6. Determination of distance to concentration results for the identified7 Findings & Conclusions

Figure 1:Vent Dispersion Analysis Methodology Flow sheet<br>

1. Selection of Damage Criteria

As per the objective of the study to understand the impact of flammable and toxic impacts due to dispersion of material released from atmospheric vent and cold venting from flare, below mentioned concentration are analyzed for impact in downwind direction and on ground level:

• For flammable gas dispersion – LFL, 0.5LFL and 0.1 LFL
• For toxic gas dispersion – IDLH and 0.5 IDLH.
  • Project Deliverables

Table 1:Vent Dispersion Analysis Study

Sr. No.	Document Deliverable
	Executive Summary
	Objective
	Scope of work
	Vent Dispersion Analysis Methodology
	Identification of Release Scenarios
	Dispersion Study Results
	Study Assumptions
	Gas dispersion graphs
	Conclusion
	Comments Parking Sheet

• Guideline Used for Vent Dispersion Analysis Study
• API-521, Pressure-relieving and Depressuring Systems

• Software to be used
• PHAST/Safeti software.