Emergency Plume Risk Plotting with Plumecast & WindSonic
Around the world there are a large number of processes being carried out at manufacturing facilities or chemical plants etc. that can be harmful to the workers and the local population. Caution needs to be taken with these types of processes in not only avoiding spills in the first place but also in understanding where smoke or gases in the form of a “plume” may travel to if there is ever an issue at the plant i.e. a spill.
Product update: MetStream has been discontinued. This note is kept for reference. For current data and display options, speak to our team.
A large number of facilities simply look to local forecast sites, direction flags, windsocks or even the direction of smoke rising from other industrial plants to indicate wind flow when an issue arises. However, this is not always acceptable to the authorities who will have to provide emergency response if there is ever an issue and so Plumecast has been developed using its own unique dispersion models to assist individual facilities and authorities.
What is Plumecast?
Plumecast provides a real time display of possible and actual dispersion of atmospheric pollutants in an accidental release. It shows emergency services, site operators and incident managers the area at risk from any toxic releases into the atmosphere to help them implement appropriate emergency procedures.
Plumecast is a combination of a simple dispersion model and fast response anemometers. A PC monitor displays the area that would be at risk from an accidental release and in an emergency it displays the estimated present location of an airborne plume and areas at risk from its further spread.
The use of real-time measurements taken at or near the source of the release is the key feature of Plumecast and gives it not just greater accuracy but a unique ability to react to changing circumstances.
The system can be used for both emergency situations and continuous and operational risk assessment.
For risk assessment two lines are drawn from the potential pollution source over a map of the local area. These enclose an ‘area at risk’, the area over which airborne pollution might pass in the event of a release. These lines are updated continuously even when there is no actual release so that in the event of an accident the area at risk is instantly available. Therefore there is no delay in starting dispersion models and this information is available and can be used in advance of off-site agencies responding.
How is Plumecast set-up?
Plumecast is a combination of software running a dispersion model on a PC and a wind sensor providing realtime wind data every second.
PC running Plumecast software
displaying risk area in real time
Data stream in NMEA 0183 format
via. RS-232, RS-485 internet etc.
Wind sensor on or
near risk site
This data is also combined with knowledge of the source site location, date and time of day to make assessments of likely variations in wind through the depth of the atmospheric boundary layer. Please discuss site installation considerations for Plumecast directly with Met Engineering Ltd.
User Software Display
Plumecast is intended to give real-time displays of both area at risk and, optionally, the position of a plume if a release does occur. The area at risk is shown by lines, the best estimate of the area the plume has reached is plotted as it happens in real time. To assist incident managers ‘range rings’ are drawn to indicate how far the plume is likely to travel in a ten minute period. The picture below shows a plot drawn using Plumecast.
As an option a large icon is used to start plotting of a real plume. It can also be used to stop the emission. In this case Plumecast will continue to plot the movement of the material already released.
The display also shows various alarms. These
include warnings of missing data, light winds or ‘marked discontinuity’. A marked discontinuity alarm means that there has been a major and sustained change in wind direction or speed within the last 10km run of wind. In these conditions Plumecast only takes into account data back to this discontinuity. If winds are very light then the display is ‘frozen’ and the light wind alarm icon is lit.
The display allows an operator to specify plume
density. A site using chlorine for example would probably only use the ‘dense’ option but a severe fire at a chemical warehouse might need ‘dense’ ‘neutral’ and ‘buoyant’ set. Current wind data is also displayed. This is based on a representative run of wind rather than an instant snapshot of varying wind speed and direction that could be very misleading.
User Software Features
The most important feature of Plumecast software is that the use of real time data from the incident location allows it to react to changes in conditions during an incident. It also means that Plumecast can react to local winds such as sea breezes or katabatic flows, which can be missed if larger scale models, run remotely, are used to provide guidance.
As visualisation is very important, the image below shows the dispersion model run on real wind data and after the ‘plume’ had travelled about 3 km the wind had veered clockwise. At this point the plotting colour was also changed to show how Plumecast copes with this situation.
The development of Plumecast takes a ‘fail-safe’ approach. For example the plume displayed during an incident includes not only the area where the plume is but also the area where it has been. This is because some pollutants can leave an area hazardous even when the plume has been moved away by a change in wind direction. The area at risk can be limited to some extent if the user can specify whether the released material is denser than air, of neutral density or buoyant.
In addition to local displays Plumecast can be configured to give XML format output representing the area at risk. This allows information to be shared with other emergency response software and GIS systems.
Factors considered by Plumecast
The position of the area at risk lines is determined by a number of factors including the current conditions measured by the sensors, both mean wind and turbulence characteristics. Plumecast uses recent wind data up to the last 10km run of wind.
There are also allowances for likely wind shear through the boundary layer and the change in wind direction that is likely in a given time. These are themselves dependent on the current conditions and are often neglected by other plume modelling systems.
The area at risk is constantly re-calculated as conditions change. For example, statistically the change in mean wind direction that is likely in a given time depends on wind speed; in simple terms stronger winds are less likely to change than light winds. This allows Plumecast, using empirical rules, to constantly adjust the area of risk accordingly. In a similar way allowances for wind shear, both in speed and direction, are assessed using established relationships connecting it to latitude, surface roughness, wind speed and atmospheric stability. Plumecast uses time of day and site location to calculate local sunrise and sunset which are used in these assessments.
Plumecast makes an allowance for the roughness of local terrain with an overall accuracy figure of 85%, which is primarily based on the statistical chance of a significant wind direction change in one hour. Plumecast includes a factor allowing for the likelihood of wind direction changes (a function of wind speed) and the area at risk lines can be relied upon for periods up to 30 minutes. Note that the area at risk lines will be adjusted during this time anyway.
Plumecast has already been installed
successfully at a Chemical storage depot in Cambridgeshire “H.W. Coates Ltd is pleased with Plumecast which we have incorporated into our off-site emergency plans and procedures.”
Why GILL?
GILL’s range of 2-axis anemometers provide wind speed (WindSonic plastic & metal to 75m/s and stainless steel WindObserver up to 100m/s) and direction (360°) measurements in robust, polycarbonate, aluminium or stainless steel housings giving high quality, reliable fit-and-forget installations. Having no moving parts with high, long-term accuracy they offer clear advantages over conventional cup-and-vane instruments, particularly in such exposed, salt laden environments. WindSonic and WindObserver provide the industry standard NMEA 0183 output compatible with Plumecast.
Please contact: Met Engineering Limited, United Kingdom, Tel: +44 (0)161 737 2627, E-mail: info@metenguk.com
Originally published as a Gill application note (AN0053).
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