DEFENSE SIGNALS!

BY FRED H. ARNOLD,
REGIONAL FORESTER.

"That fire burns is one of the first lessons of childhood." Acquired later is a knowledge of fire behavior, as through experience one observes that when it is dry and windy fires start more easily and spread more rapidly. Add to these weather and fuel conditions the factor of risk - presence or absence of an igniting agency - and you have the substance of what is meant by fire danger.

When it has not rained for two or three weeks, with little moisture in the air and perhaps a warm dry wind blowing, burning conditions in fields and woods react accordingly and become correspondingly dry. These conditions are plainly evident when dead leaves in the forest crackle with brittle sounds underfoot and field grasses swish and rustle against passing feet. Then it may be said the fire danger is high in locations where, due to one cause or another, fires are likely to flare up unexpectedly.

How dry is "high fire danger" and how much more severe is "very high" or "extremely high fire danger? Does an individual estimate the degree of fire danger consistently on the same basis on different days? And does the term "high fire danger" convey the same meaning to one person as to another? Unfortunately the use of comparative adjectives is too indefinite and too subject to varying individual interpretation to express definite degrees of a condition such as fire danger. To appraise and rate fire danger accurately and on an absolute rather than on a relative basis is a problem which has now been solved successfully by the United States Forest Service through the work of several of its Forest Experiment Stations.

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The basic system that has been developed is now in use throughout the country in national and state forests and parks and in other types of areas in public and private ownership. Briefly it consists of measuring those few weather and fuel conditions which substantially influence fire danger. These measurements are correlated in a slide-rule type of scale known as a Fire Danger Meter. The integrated result obtained from this meter is a simple number from 1 to 5, or to 6 to 7 in classifications used in some parts of the country. Fire Danger Class 1 means low or nonexistent fire danger. Fire Danger Class 5, 6, or 7, depending up on the classification in use, represents an extremely high degree of danger.

The mere knowledge of the class of fire danger will not of course prevent or put out fires. This reliable and definite knowledge is only as good as it is effectively applied to the specific problem of protecting an area against fire. For instance, good use is made of the information when the fire fighting organization is stepped up or reduced in accordance with the fluctuations in the readings. Fire lookout stations can be manned or left unattended as the danger conditions prescribe. Forests may be closed entirely to public use when the highest class of fire danger is reached, and in parks certain forms of use such as fishing, or habits such as smoking except in designated places may be prohibited. Debris burning and other work activities which may increase fire risk are ordinarily stopped while the high numbers are recorded.

On the premise that increased cooperation from park visitors in the matter of fire prevention is cultivated by informing them of current fire danger conditions various devices have been made and used to present the facts in an impressionable and understandable manner. Acadia National Park's answer is the Forest Fire Warning board pictured on page 16. This board indicates the fire danger class for the day, explains briefly what each of the 5 classes means, and prescribes the corresponding fire prevention precautions that should be observed. Posted in public camp grounds, picnic areas and at other points where people are most likely to see them, it has been observed that these boards arouse curiosity. and lead people to explore their meaning. Displayed in this manner, the boards frequently prompt questions above fire protection in the park and stimulate fire consciousness on the part of visitors and employees alike. If devices of this sort can provoke in the minds of those who observe them a stronger realization of the need for exercising greater care with fire they must be considered as effective forest fire prevention media. The board shown here has demonstrated its value in this respect at Acadia National Park.

Acadia's Fire Invasion Threat is Posted Daily