702 
Journal o f Agricultural Research 
Vol. XXX, No. 8 
3. The causes of fire may be classified 
as “general” or “blanket” risks, and 
“special” or “local,” sometimes called 
“fixed” risks. The latter include such 
causes as railroads, lumbering opera¬ 
tions, and brush burning, whose loca¬ 
tions are definitely fixed within certain 
restricted known localities. Some 
camper fires might also be included in 
this class, because they are localized 
along established travel routes or at 
established camp sites. Since, however 
the data contained in the fire records 
do not permit segregation of such fires 
from the other camper fires, they are 
all thrown together with fires caused 
by lightning, incendiaries, miscellan¬ 
eous, and unknown causes, into the 
general risk class, which includes those 
fires that may occur practically any¬ 
where within a forest unit. 
For the purpose of rating the general 
hazard of given regions and forest types, 
only these general risks were considered. 
Rating of special risks will have to be 
done for each unit individually, accord¬ 
ing to the kind, extent, and location of 
of the fixed causes of fire within or 
adjacent to it, and according to the 
character of forest covering the parti¬ 
cular parts of the unit exposed to such 
risks. 
CHARACTER OF RATING 
The rating of risks for different types 
within each of the 21 subregions was 
based on the following considerations: 
1. No data are available to indicate 
what losses might amount to without 
any protection whatever. It has some¬ 
times been stated that such data would 
afford a good measure for justifiable 
protection expenditure, but such is 
not the case. It is more important to 
know, and it is possible to learn, what 
losses may be expected with protection 
of different degrees of intensity. 
2. Intensity of protection can be 
measured best by what may be termed 
the “hour control”—that is, the time 
within which fires on a given area are 
reached. The larger the personnel, or 
the better the facilities for detection, 
communication, and travel, the smaller 
will be the hour control. Reduction 
of hour control may be expected to 
result in reduced fire loss and also in 
reduced suppression cost, but will in 
general involve also increases in the 
cost of primary protection, which will 
partly offset the saving. 
3. Data on primary protection costs 
for different types of forest and for 
protection of different degrees of inten¬ 
sity are not available nor can they be 
worked out on the basis of averages, 
but will vary according to the particular 
circumstances in each individual forest 
unit. 
4. Such general rating as can be 
made, therefore, will attempt to show 
probable fire losses and the probable 
costs of fire suppression, per unit of 
area in different forest types of the 
several regions, with protection of 
various degrees of intensity. The 
balancing of these liabilities against 
costs of maintaining the corresponding 
degrees of protection will not be 
undertaken. 
CALCULATION OF BASIC DATA FOR 
USE IN RATING 
In the first place, the records of 
individual fires were segregated by sub- 
regions and as far as possible by types 
within these regions. This could not 
be done in all cases, because of the 
incompleteness of the data contained 
in the original records. Each group of 
these records was then studied along 
the following lines. 
RELATION BETWEEN HOUR CONTROL 
AND SIZE OF FIRES 
The areas burned per fire were cor¬ 
related with the time elapsed before 
control work commenced. The purpose 
of this was to tie in the area burned 
with the intensity of protective organiz¬ 
ation. Area here means final area 
burned over by the fire up to the time 
it was extinguished; the time factor 
used is the elapsed period between 
discovery of the fire and the time when 
actual work of suppression began. 
Discovery time was used rather than 
the time when the fires started, be¬ 
cause the latter was seldom reported. 
Fires which had obviously been burning 
for a long time before discovery were 
not included in the calculations, nor 
were fires that occurred under especially 
unfavorable conditions, as evidenced 
by abnormally slow spread. It is well 
known that fires usually spread very 
slowly, often hardly at all, during the 
night, and suppression crews usually 
can not get to a fire as fast at night as 
during the day. For these reasons, in 
order to put all the elapsed periods on 
approximately the same basis, the hours 
between 9 p. m. and 6 a. m. were rated 
at only half the actual elapsed time. 
Fires were grouped according to 
elapsed periods—e. g., less than 1 hour, 
1 to 2 hours, 2 to 3 hours, etc.; and the 
elapsed times and final acreages for the 
fires in each group were averaged and 
plotted as abscissae and ordinates, 
