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MConline SAC Interim Statement released

BRADES: The Volcano Executive Group (VEG) on Monday decided to defer any further decision on the Day Time Entry Zone (DTEZ) until the full Scientific Advisory Committee (SAC) assessment is available.

The full SAC Report, according to the VEG, is expected by the end of this month and will be available to to public. Individuals on the island with queries about the Interim (SAC) Statement will be able to raise them at a public meeting with MVO scientists scheduled for the Vue Pointe Hotel on Tuesday evening.

Scientific Advisory Committee

on Montserrat Volcanic Activity

Interim Statement of 18 March 2004

1. We had intended to release our Main Report on the assessment of the hazards and risks associated with the Soufrière Hills Volcano about now. However, because of the elevated level of activity at the volcano since 3 March we have decided to defer the full Report and to issue this Interim Statement instead. This is because the latest monitoring evidence suggests that there is the possibility that a new dome may begin to grow very soon. If the dome does grow soon and we can determine the initial rate of growth of the dome then that will enable us to produce a better informed Report, one which will be of more practical use in the months ahead. That said we anticipate providing our Report within two weeks from now.

2. We recognise that the issue of safety within the DTEZ is one of pressing concern. Hence in issuing this statement we are restricting our thoughts to the risks within the DTEZ as an entity. The main report will deal with the risk issues relevant to more localised areas within the DTEZ and the rest of Montserrat.

3. Firstly, we consider the situation as it is now for the DTEZ, with no dome growing, some moderate level activity including occasional ash venting and restrictions to daytime entry applicable. The hazards faced are of possible sudden explosions with fallout of ash and rocks and also a large sudden explosion with pyroclastic flows generated by column collapse. The likelihood of any of these hazards, particularly the second, is small and for the DTEZ with daytime entry restrictions the corresponding risk exposure is in the lower part of the LOW category on the CMO's scale (see Appendix).

4. Next, we consider the situation in which 200 people might be living, full-time, in the DTEZ in Cork Hill, Richmond Hill and Fox's Bay but still under the current state of the volcano. The potential hazards are the same, and while the average individual risk remains in the LOW category, it would now be at the upper end, bordering on MODERATE.

5. Finally, we assume that dome growth resumes. Then for several months at least, no hazards from pyroclastic flows derived from dome collapse will be possible within the DTEZ. However the probability of hazard from fallout and pyroclastic flows from column collapse, as above, will increase slightly. Also the probability of these hazards occurring will be further increased if the rate at which lava is supplied to the volcano is high. For low average dome growth rates, such as those seen in the first half of 2003, the risk exposure in an occupied DTEZ for a typical individual could be LOW to MODERATE, but for high dome growth rates, such as those seen in the second half of 1997, the risk levels could easily (and rapidly) switch from upper MODERATE to HIGH.

6. All these risk estimates represent our best scientific judgement at the present time, given the past behaviour of the volcano and the information and observations that are available. There are limitations and uncertainties involved. If the levels of individual risk exposure in the DTEZ are to be used to inform public safety decisions then an analysis done on a more precautionary basis (i.e. incorporating some additional element to allow for the margins of uncertainty) could easily provide rankings higher on the CMO's Scale than those quoted above. Thus, given the limitations intrinsic in risk assessment, but mainly because of the potentially large range of risk exposure in the DTEZ that is contingent upon the rate of supply of lava, we would urge caution in any decision making concerning the long-term status of that area. Once the effusion rate of lava is known (if indeed it does resume at the surface), then the level of hazard becomes much more apparent and the risk exposure much better constrained, enabling more informed decisions to be made.

Appendix: Chief Medical Officer's Risk Scale

Negligible: an adverse event occurring at a frequency below one per million. This would be of little concern for ordinary living if the issue was an environmental one, or the consequence of a health care intervention. It should be noted, however, that this does not mean that the event is not important - it almost certainly will be to the individual - nor that it is not possible to reduce the risk even further. Other words which can be used in this context are 'remote' or 'insignificant'. If the word 'safe' is to be used it must be seen to mean negligible, but should not import no, or zero, risk.

Minimal: a risk of an adverse event occurring in the range of between one in a million and one in 100,000, and that the conduct of normal life is not generally affected as long as reasonable precautions are taken. The possibility of a risk is thus clearly noted and could be described as 'acceptable' or 'very small'. But what is acceptable to one individual may not be to another.

Very low: a risk of between one in 100,000 and one in 10,000, and thus begins to describe an event, or a consequence of a health care procedure, occurring more frequently.

Low: a risk of between one in 10,000 and one in 1,000. Once again this would fit into many clinical procedures and environmental hazards. Other words which might be used include 'reasonable', 'tolerable' and 'small'. Many risks fall into this very broad category.

Moderate: a risk of between one in 1,000 and one in 100. It would cover a wide range of procedures, treatment and environmental events.

High: fairly regular events that would occur at a rate greater than one in 100. They may also be described as 'frequent', 'significant' or 'serious'. It may be appropriate further to subdivide this category.

Unknown: when the level of risk is unknown or unquantifiable. This is not uncommon in the early stages of an environmental concern or the beginning of a newly recognised disease process (such as the beginning of the HIV epidemic). (March 22, 2004)

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