Hazard prioritization

Why prioritize hazards?

In any community, resources for the management of hazards, vulnerability, and emergencies are limited. With the best of intentions, the constraints of time and money preclude protecting people, property, and the environment from every hazard. Therefore, it is crucial to decide which hazards should be dealt with most urgently and which should be dealt with later or not at all.

How to prioritize hazards

Determining which hazards to target for management is called “hazard prioritization”, or “hazard ranking”. There are a number of ways to prioritize hazards, two of which are discussed in the following paragraphs.

The key to prioritizing hazards is community involvement. As in the other steps of vulnerability assessment, consultative and participative processes are necessary. The commitment of those required to take action and those who may be affected by hazards is essential. Without it, the best emergency management strategies, based on the best of vulnerability assessments, may fail. Hence, the first step is to involve the relevant people.

Another reason for using consultative and participative processes in hazard prioritization is that the choices that need to be made to reduce the likely effects of hazards are political decisions. Some hazard mitigation and response strategies will only protect some people and others may not address the needs of the most vulnerable. The decisions as to who and what should be protected, and to what degree, should be made by the whole community.

The second step is to determine which criteria to use to rank the hazards. Criteria may include factors such as the probability of an emergency, the level of vulnerability of people or property or both, the degree of manageability, and whether the hazard may worsen and how quickly. There are a number of methods that use such criteria, including the FEMA (the United States Federal Emergency Management Agency) model and the SMUG (“seriousness”, “manageability”, “urgency”, and “growth” - developed by the Tasmania State Emergency Service) hazard priority system, which are described below.

A simpler method has already been described in the section on hazard identification - the group technique for identifying hazards. Using this technique and a few simple criteria such as “risk” (the likelihood of a given level of harm), “manageability” (whether anything can be done about this hazard), and “vulnerability” (how damaging is the potential harm caused by this hazard), it is possible to rank community hazards. Community vulnerabilities can also be ranked in this way.

In prioritizing hazards there is no “right” answer, and there will be a number of hazards that are considered to be more serious than others. It may also be difficult to equate or compare different hazard analysis results. This is to be expected, since different hazards may have very different effects, and it is not always possible to compare hazards precisely. In short, resources should be committed to hazards that the community considers to be most serious, using whatever criteria of “seriousness” they deem correct. Hazard prioritization should be used as a guide to decision-making and modified to suit the requirements of particular communities.

The FEMA model

The FEMA model uses four criteria in an evaluation and scoring system - history, vulnerability, maximum threat, and probability (12):

· History. If a certain type of emergency has occurred in the past, it is known that there were sufficient hazardous conditions and vulnerability to cause the event. Unless these conditions no longer exist, or have been substantially reduced, a similar emergency may occur again. Lack of a past occurrence, however, does not mean that there is no future emergency potential.

· Vulnerability. This attempts to determine the number of people and the value of property that may be vulnerable, based on such factors as vulnerable groups (aged, disabled, and children); population densities; location of population groups; location and value of property; and location of vital facilities, e.g. hospitals. Overlaying hazard maps on a map of the community assists in this process.

· Maximum threat. This is essentially the worst case scenario; that is, it assumes the most serious event possible and the greatest impact. It is expressed in terms of human casualties and property loss. Secondary events (such as dam failure following an earthquake) also need to be considered.

· Probability. Probability is the likelihood of an event occurring, expressed in terms of chances per year that an event of a specific intensity (or greater) will occur. There is some link between probability and history; however, since some hazards are without historical precedent, an analysis of both history and probability is necessary.

An evaluation of low, medium, or high is made for each criterion shown in Table 15.

For each evaluation, score the following:

Low	1 point
Medium	5 points
High	10 points

Some criteria have been determined as more important than others, and the following weightings have been established:

History	× 2
Vulnerability	× 5
Maximum threat	× 10
Probability	× 7

A composite score for each hazard is arrived at by multiplying the score by the weighting, then adding the four results. Table 16 gives an example:

The FEMA model suggests a threshold of 100 points. All hazards that total more than 100 points may receive higher priority in emergency preparedness. Hazards totalling less than 100 points, while receiving a lower priority, should still be considered.

This process should be repeated for all identified hazards and for a range of scenarios with the same hazard.

Table 15. The FEMA evaluation and scoring system^a

Criteria			Evaluation
History: whether an emergency event has occurred:		<2 times in 100 years	Low
		2-3 times in 100 years	Medium
		>3 times in 100 years	High
Vulnerability:	of people	1%	Low
		1-10%	Medium
		>10%	High
	of property	1%	Low
		1-10%	Medium
		>10%	High
Maximum threat: area of the community affected		5%	Low
		5-25%	Medium
		>25%	High
Probability: chances per year of an emergency		<1 in 1 000	Low
		1 in 1 000-1 in 10	Medium
		>1 in 10	High

^aReproduced from reference 12 by permission of the publisher, Emergency Management Australia (formerly Natural Disasters Organisation).

Table 16. Sample use of the FEMA evaluation and scoring system

Criteria	Evaluation	Score × weighting	Total
History	High	10 × 2	20
Vulnerability	Medium	5 × 5	25
Maximum threat	High	10 × 10	100
Probability	Medium	5 × 7	35
Total			180

SMUG hazard priority system

The SMUG hazard priority system allows a direct comparison of a number of possible hazards, through ratings of high, medium, or low, against four separate criteria common to all hazards (12):

· Seriousness. The relative impact of a hazard, in terms of financial cost or number of people affected or both. If a hazard represents a threat to the greatest number of people or would cost the most (or both), that hazard is given a “high” rating. All identified hazards are rated as “high”, “medium”, or “low”, in terms of seriousness. If the group cannot agree, the highest rating should be given.

· Manageability. “Can anything be done about the hazard?”. If the impact of the hazard can be lessened, the rating for manageability would be “high”. If it were manageable only after it had occurred, the rating would be “low”.

· Urgency. “High” means that something should be done now, “medium” means something should be done in the near future, and “low” means there is no urgency and action can be deferred.

· Growth. If nothing is done about the hazard, will it grow worse or remain as it is? If the hazard would increase quickly, it is rated “high”, if it would grow gradually, “medium”, and if it would stay static, “low”.

Once a relative rating has been allocated to all identified hazards according to these criteria, the list of hazards should be reviewed. Those with the most “high” ratings are the ones that warrant priority attention. It is very important to provide clear evidence to support the ratings. Table 17, for example, would be useful for recording decisions.

Example of use of prioritization techniques

There is a basic difference between the FEMA and SMUG hazard priority systems. In the FEMA model, each hazard is rated individually, using a number of quantitative criteria such as history and probability, and individually given a numerical score, based on the value of each of those criteria. The SMUG system, on the other hand, compares hazards directly using a number of criteria, in a stepwise fashion, and is qualitative.

Table 17. The SMUG hazard priority system^a

Criteria
Hazard	Seriousness	Manageability	Urgency	Growth
Hazard A	H/M/L	H/M/L	H/M/L	H/M/L
Hazard B	H/M/L	H/M/L	H/M/L	H/M/L
Hazard C	H/M/L	H/M/L	H/M/L	H/M/L

^aReproduced from reference 12 by permission of the publisher, Emergency Management Australia (formerly Natural Disasters Organisation).

The FEMA model, because it judges each hazard individually in a numerical manner, may provide more satisfying results than the SMUG system if there are sound numerical data on the hazards in question. The SMUG system, on the other hand, allows close comparison of each hazard with the others on the basis of the given criteria and therefore allows a closer examination of the differences between hazards in a more holistic sense.

In the following example of prioritization, the possible effects of hazards that exist in and near a fictitious country town are summarized.

Example

The town is situated near a river and bordered on one side by a forest. It has a population of approximately 1200 people, evenly spread throughout the town. Most families have vehicles, there are no care homes for the elderly, and there is one school. The townspeople all speak the same language, have a similar cultural and ethnic background, and consider themselves self-sufficient in most respects. The town’s economy is based on providing services to the surrounding rural community and there are also a few light industries. There is a strong feeling of pride in the town, and there are a number of active community groups. The town is the seat of local government for the area, but the services the local government provides mostly relate to road maintenance, garbage collection, and sewage disposal. The local government has not developed any emergency management strategies.

The river floods regularly, and major flooding has occurred about once every 40 years for the past century. Alterations to the environment upstream suggest that flooding may be more extreme in the future. Major floods have the potential to destroy the sewage treatment plant and contaminate water supplies, incapacitate all telephone and electricity services, destroy most bridges in the area, and cover many roads, forcing the evacuation of about 15% of all homes and disrupting half the town’s light industries. It is not thought likely that many residents would be killed by floods while in their homes or during evacuation, but it is possible that some may be killed using flooded roads. A major flood has not occurred for many years and most residents do not perceive flood as a serious hazard.

The forest adjacent to the town is fairly dense and subject to selective logging. There have been frequent forest fires, some of which have threatened houses on the forest side of the town. The vegetation in the fields surrounding the town is generally kept low by grazing animals, but there are periods in summer following heavy rains when there is considerable growth of grass, which then dries. There is an active fire service in the town, but it is called only infrequently to fires. Telephone and electricity services may be disrupted by a severe fire and about 5% of houses may be burnt, but deaths and injuries are likely only among firefighters and during evacuation in the event of a serious fire. Geologists believe the area to be potentially subject to earthquakes, with a 10% chance of exceeding modified Mercalli VII intensity in a given 50-year period. The area has experienced one severe earthquake in known history, but this occurred before the town’s construction, when the first settlers had only just arrived. Half of the town is built on alluvial soils that may be prone to liquefaction. Most buildings are of medium-quality masonry and timber construction, so that there is not much likelihood of building destruction or of a large number of deaths. The greatest risk is the destruction of all electricity, telephone, water supply, and sewage services, partial destruction of most bridges and many roads, and long-term disruption to light industry. There is no local knowledge of any earthquake hazard.

The town is almost totally dependent on the economic success of the surrounding rural areas - the raising of livestock for domestic consumption, for live export, and for export as meat products. There is a rudimentary quarantine system in place for the entire country, but no planning for response to an outbreak of exotic disease among livestock. An uncontrolled outbreak of such a disease would lead to the quarantining of the entire country and an immediate end to all animal product exports. This would cause an almost immediate closure of most businesses in the town, resulting in widespread bankruptcy and unemployment. It is highly unlikely that the disease would be a direct cause of human deaths or injuries. Local farmers and veterinarians are aware of the possibility of exotic animal disease, but unaware of the possible implications of an uncontrolled outbreak.

Using the SMUG hazard priority system

How would the SMUG system prioritize the four hazards of flood, forest fire, earthquake, and exotic animal disease for this town, based on the information given in the example? Table 18 shows a possible prioritization.

To summarize the SMUG prioritization, the hazards should be ranked in the order shown in Table 19.

Using the FEMA model

Using the FEMA model to prioritize the hazards described in the example produces the results summarized in Table 20.

To complete this FEMA prioritization, a number of assumptions have been made about the frequency and consequences of an event; in a real analysis these assumptions would have to be explicitly written down. According to the principles of the FEMA model, where a score in excess of 100 suggests that management of that hazard is required, the earthquake hazard would not be considered particularly serious compared with the other three.

Comparing FEMA and SMUG results

Table 21 compares the FEMA rating with the SMUG rating for the hazards described in the example.

Table 18. Sample use of SMUG hazard priority system

Criteria
Hazard	Seriousness		Manageability		Urgency		Growth
Flood	May cause some deaths, will cause considerable inconvenience and property if there is no control of and services damage	H	Manageable in that future developments can be protected from flood damage and response plans can be developed	H	As major floods occur infrequently, may not be considered too urgent by some	M	This problem will become significantly worse development in the flood plain	M
Forest fire	May cause some deaths, some property and services damage	M	Hazard reduction and fire breaks may completely eliminate the threat	H	Moderately urgent, but will be more urgent during dry season	M	If hazard reduction measures are not undertaken this hazard may become worse	L
Earthquake	Will destroy services, therefore economic and social costs will be high	M	May not be cost-effective to mitigate effects by structural means; response and recovery plans would alleviate effects	L	Currently impossible to predict, but probably an infrequent occurrence; overall impact over the years is low	L	Will not become a greater problem if not addressed now	L
Exotic animal disease	Will cause extreme social and economic disruption; many effects may be irreversible	H	Can be managed with good quarantine procedures and effective response procedures	H	Because of serious consequences should be addressed as soon as possible	H	Will not become a greater problem if not addressed now	L

Table 19. Sample hazard rating

Hazard	SMUG prioritization
Flood	2
Forest fire	3
Earthquake	4
Exotic animal disease	1

Table 20. Sample use of the FEMA model

Criteria	Flood	Forest fire	Earthquake	Exotic animal disease
History	(medium)	(high)	(low)	(low)
	5 × 2 = 10	10 × 2 = 20	1 × 2 = 2	1 × 2 = 2
Vulnerability	(high)	(medium)	(medium)	(high)
	10 × 5 = 50	5 × 5 = 25	5 × 5 = 25	10 × 5 = 50
Maximum threat	(medium)	(low)	(medium)	(high)
	5 × 10 = 50	1 × 10 = 10	5 × 10 = 50	10 × 10 = 100
Probability	(medium)	(high)	(low)	(medium)
	5 × 7 = 35	10 × 7 = 70	1 × 7 = 7	5 × 7 = 35
Total	145	125	84	187

Table 21. Comparison of hazard ratings

Hazard	SMUG prioritization	FEMA prioritization
Flood	2	2
Forest fire	3	3
Earthquake	4	4
Exotic animal disease	1	1

The two prioritization systems may, in reality, provide different rankings because they use very different criteria, and some variation between their results would be expected. Experience has shown, however, that they tend to produce similar results.

It therefore seems that exotic animal disease is the greatest hazard for the town in the example, with flood coming second. Most of the hazards for this town are relatively minor since there is little expectation of loss of human life, but there are some significant economic implications.