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S-100 A ~ Annual Safety Refresher
S-100 A ~ Part One, Sections 1-5
Fire Behaviour
1 - Types of Fire
Subsurface fires, burning in the duff, partially decayed leaves and woody material do not pose a great safety hazard to fire fighters. Be careful not to step into burnt out root or stump holes. A hazardous condition may exist where large quantities of dead or dried material have accumulated. If fire extends into this material the fire may spread quickly and entrap the fire fighter.Surface fires, burning in the ground vegetation, slash, windfalls, young trees and the lower branches of standing trees pose a greater hazard to fire fighters. Be careful of radiant heat generated by the fire, flare ups, smokey conditions, poor visibility, sudden shifts of the wind and possible entrapment. Heavy accumulations of ladder fuel can permit the fire to rapidly extend into the crowns of the trees. Crew safety procedures should be re-evaluated if there is a lot of ladder fuel present.
Crown fires burning in the tops of trees and jumping from tree to tree, create extremely dangerous conditions to work in. The fire fighter should not attempt to attack a fire once it has started to burn in the crown. Leave the area and retreat to the nearest safe area by way of pre established escape routes. If a single tree burns to the top, firefighters should back away and reassess the situation because this candelling effect can initiate a running crown fire.
2 - Fuel Types
Caution should be exercised in proportion to the type, quantity and moisture content of the forest fuels. Wet fuels (high moisture content) will not generate the same heat intensity as will dried fuels.Areas of heavy fuel accumulations will be more hazardous than areas with less fuel loading. Areas where the fuels are large will produce more heat and will sustain the heat longer than areas with small fuels such as grass, brush and hardwood trees, also known as deciduous trees.
Hardwood (deciduous) trees will burn with less intensity and at a slower rate than softwood (evergreen) trees.
3 - Other Factors Influencing Fire Behaviour
Weather is a dominant factor in fire fighting safety. Hot, dry and windy conditions are far more dangerous than cool, moist conditions with little or no wind. Exercise caution as weather conditions change for the worse. If a wind event is predicted, the fire dispatcher will issue a weather advisory to all crews in the field. Be prepared to abandon fire fighting efforts if high wind conditions occur. Always be aware of weather conditions and plan operations with them in mind. Fire behaviour will normally be more aggressive as the day progresses into the afternoon.Slope can have a dramatic effect on fire behaviour. Fire will move up a slope at a far greater speed than fire on the flat. Be aware of daily afternoon up slope winds and evening down slope winds. Working on a steep slope requires a lot of extra personal energy and the firefighter will move much slower making entrapment a greater risk.
Aspect will effect the quantity, type and moisture content of the forest fuels. A southern exposure will have drier fuels whereas the northern exposure will be cooler and have a higher moisture content. Never let the aspect distract the firefighter for exercising caution at all times.
Topography will effect how hard it is to access the fire. Exercise extra caution when crossing steep side slopes or areas of loose rocks. Never work directly below anyone else on a steep slope. If you knock a rock or log loose and it starts to roll down the hill, yell "rock". If you feel you are in the path of a rolling object, do not look up, but immediatly protect yourself by staying low to the ground or behind a tree or large rock. In mountainous country, fire fighters should be aware of the chimney effect. This is where a fire will rush up a gully or valley with great speed potentially trapping anyone working above.
4 - Fire Ranking System
In order for the firefighter to better understand the fire conditions they will encounter, this general ranking system will give them a picture of what the fire looks like, depending on fuel types.
Rank 1 Smoldering ground fire or slow moving surface fire. Little or no flames.Rank 2 Low vigor surface fire in grass and brush. Flames up to your knees.
Rank 3 More aggressive ground fire in brush and lower limbs. Flames at 1-2 mtrs.
Rank 4 High vigor fire burning on surface and into some tree tops. Flames over 2 mtrs.
Rank 5 Extreme surface fire and running from crown to crown. Flames in tree tops.
Rank 6 Total blow up or conflagration. All trees on fire. Fire above tree tops.
Fire fighters will not attempt to control fires greater then a rank 3 blaze unless otherwisw directed by the supervisor.
5 - Chain of Command
The chain of command is a key factor in safe fire fighting. Every fire fighter has only one boss (aka. supervisor or crew leader). Know who your crew leader is and listen to them at all times. Never leave a work area without permission. If you are asked to perform a task that you are not trained to do, or feel you do not have the proper safety gear, or believe the task to be unsafe, inform your crew leader of the situation.
Questions for Sections 1-5
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