Risk contour

Figure 26-7 is an example of an individual risk contour plot, which shows the expec ted frequency of an event causing a specified level of harm at a specified location, regardless whether anyone is present at that location to suffer that level of harm. 

A method for graphically displaying individual risk results is use of the risk contour, or risk isopleth. If individual risk is defined as the likelihood of someone suffering a specified injury or loss, then individual risk can be calculated at particular geographic locations around the vicinity of a facility or operation. If the individual risk is calculated at many points surrounding the facility, then points of equal risk can be connected to... 

The F-N curve, the risk profile, and the risk contour are the three most commonly used methods of graphically presenting risk results. Normally, you will elect to use more than one of these methods when evaluating risk estimates for decision making. 

FIG. 23-28 Example of an individual risk contour plot. (CCPS-AIChE, 1989, p. 269.)... 

In addition, there were other benefits such as product quality, elimination of mercury emissions and reduced risk contours emanating from the plants. 

The plant is located in a rural area some 10 km out of Gladstone and the nearest resident is many kilometres away. Pressurised chlorine storage tanks are used and the risk contours are such that there is no reason to alter this configuration. 

Risk contour—Lines that connect points of equal individual risk around the facility. 

INDIVIDUAL RISK Individual Risk Contour Illustrated geographical distribution of individual risk gives indication of number of people at various risk levels Very time-consuming to produce along an entire route... 

Similar to a risk contour for a fixed facility, a risk transect can be used to determine whether a sensitive population (such as a school or hospital) along the route falls within a high-risk area. 

Risk Contour Lines that cormect points of equal individual risk arorrrrd the facihty ( iso-risk lines). 

In addition to indicating numerical values pictorial representations of risk are used. By way of example Fig. 8.5 shows the location risk as lines on a map. These lines around the investigated plant are lines of equal risk, the so-called iso-risk contours. 

Fig. 8.5 Iso-risk contours in the surroundings of an industrial site (DSM Geleen) (courtesy of [19])...

The individual risk (called location-based risk in the Netherlands) is defined as the risk to an (unprotected) individual at a specific location. The risk is expressed as the probabihly of fatality in one year as a direct result of an on-site incident involving hazardous substances. The individual risk is visualized by risk contours on a map. The risk for the location of vulnerable objects is limited to a maximum of 10 per year. Examples of vulneiable objects are dwellings, schools and hospitals. For less vulnerable objects, e.g. small offices, the individual risk contour of 10 per year is a target value. 

Societal risk calculations have been performed with large population densities - up to 255 persons per hectare - outside the individual risk contour of 10 per year for Class 1 flammable hquids. Even for these densities, no societal risk was calculated as the mnn-ber of victims N stays below the minimum value of 10 (see Paragraph 1). 

The introduction of the new zoning distances will lead to about 70 locations where vulnerable objects are situated within the individual risk contour of 10 per year. This corresponds with 3 kilometers of pipeline that will cause potential bottleneck situations. Only dweUings in areas with a density of more than two per hectare have been included, to avoid inclusion of isolated dwellings as these are not being defined as vulnerable objects (Staatsbiad 2004). 

A table with zoning distances was presented to the Ministry of Housing, Spatial Planning and the Environment in April 2008. The Ministry has communicated this table with instructions for use until the new legislation will be in place (Ministry ofVROM 2008). This table is based on the individual risk contours of 10 per year which have been calculated using the revised QRA method. 

Individual risk contours, which show the variation of risk around a risk source generally as contours superimposed on maps... 

Individual Risk Contours (for non-directional events, the contours will be circular for directional events such as gas clouds, the contours would not be circular but more elongated along the predominant wind directions)... 

In Section 10.1, we discussed the principles of risk evaluation. With reference to that section, land use planning often involves use of individual risk contours and comparing them to guidelines such as those shown in Fig. 10.3. In some jurisdictions, the FN form of societal risk is used together with guidelines such as in Fig. 10.4. 

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