Assessment of Ventilation on Offshore Platforms

Natural ventilation can help to provide safe working conditions on offshore platforms by diluting and dispersing flammable gases and vapours. The Health and Safety Laboratory (HSL) can offer an experienced team to assess the effectiveness of ventilation on offshore platforms. This is achieved by using the team's in-depth experience of making on-site measurements and using Computational Fluid Dynamics (CFD) for ventilation assessments. The information gained by this combined approach can be used to assess and control the risks of the build up of flammable gas clouds.

The combination of on-site measurements and CFD modelling has distinct advantages over other approached. On-site measurements allow the CFD model to be validated for the specific platform. The CFD model can then be applied with confidence to give ventilation predictions over a wide range of weather conditions than are likely to be experienced during measurements made on finite number of platform visits.

Methodology
Experimental measurements are made at a number of positions in naturally ventilated modules using ultrasonic anemometers to give local air speed and direction. All measurements are correlated with the wind speed and direction. As ventilation rates in naturally ventilated modules are generally not uniform, the technique enables areas of low air speed to be identified. Ventilation in enclosed or mechanically ventilated areas can also be assessed using tracer gas techniques.

A CFD model can then be used in conjunction with the wind rose data to predict the ventilation in the module for a range of wind speeds and directions. The CFD model predictions provide detailed information on the ventilation flow, such as global and local air change rates. A further advantage of the CFD approach is that it can be used to investigate and optimise suggested practical measures to improve the ventilation in relatively poorly ventilated areas before implementation on the module. It can also predict the consequences on gas cloud size via simulated gas leaks. If any measures are implemented, on-site measurements can be repeated to confirm that ventilation has improved.

Benefits of this approach:

• On-site measurements avoid uncertainties associated with a purely predictive approach
• Efficient measuring techniques minimise disruption to platform operations
• Ventilation can be assessed over a wide range of wind speeds and directions
• CFD predictions give detailed information on local ventilation conditions, and the consequences of gas leaks
• Option to use CFD to investigate and optimise possible remedial measures, in the presence of gas leaks.
• Tracer gas techniques give accurate air change rates in enclosed spaces.

HSL has used this approach as part of a research project sponsored by the Health and Safety Executive to investigate the effectiveness of natural ventilation on offshore platforms. Extensive measurements were made on three different platforms and CFD modelling was applied to one of these. The project provided detailed validation of the CFD approach and a valuable insight into the effectiveness of natural ventilation.

HSL has in-depth experience in assessing ventilation offshore: The team comprises dedicated ventilation experts and CFD engineers. The CFD engineers have experience of modelling a wide range of fluid flows including ventilation of offshore modules, gas turbine halls, fire and smoke movement and gas dispersion.

HSL's experimental and modelling capabilities cover a wide variety of applications including:

• Build-up of flammable gas clouds
• High pressure releases from failed pipelines
• Gas detection
• Fire and Explosions
• Dispersion of accidental releases of toxic gases or aerosol clouds
• Smoke movement within complex structures
• Occupational releases of hazardous substances
• Blast Waves
• Liquid Spills
• Shallow Layer Modelling
• Integral Methods
• Liquid Sprays

Further Details
Contact our Business Development Unit by telephone (+44) 01298 218218, fax (+44) 01298 218822 or email hslinfo@hsl.gov.uk.