Smokey Robertson vs Jan Braai analogy explains fire danger rating

Garth Sampson
Garth Sampson
Image: SUPPLIED

I have a technologically up to date automatic weather station that alerts me to thresholds that have been passed, one of which is the different categories of the fire danger index (FDI).

When this happens, I post the message on my Facebook Page, which led to a reader requesting an explanation about the different categories. 

The text book explanation of the FDI is that it is a rating system that provides an indication as to the fire risk for a specific area on a specific day. 

The formula uses temperature, humidity, wind speed and days since previous rain. Some models include vegetation type. 

The result will yield a category of fire risk as follows: 

Blue: 0 — 20: Safe

Green: 21 — 45: Moderate risk

Yellow: 46 — 60: Dangerous

Orange: 61 — 75: Very dangerous

Red: 76 — 100: Extreme

To explain this in simple terms, I like to use the Smokey Robertson and Jan Braai analogy.

Consider Smokey in the bottom half of the rating and Jan in the top half. 

Smokey will generally have wet wood, no firelighters or kindling and the wood will be packed tightly with little space for air movement.

Jan has his dry wood evenly spaced with plenty kindling and firelighters.

One match is all he needs to start his fire, whereas Smokey might not be successful in getting his fire going with all the matches in the world. 

The three things a fire needs to burn are heat, fuel and oxygen. 

The heat will come from a hot day (temperature), the fuel is the dry veld/bush (low humidity and a considerable period since the last rain) and oxygen which comes from a strong wind. 

Naturally strong winds assist in fanning fires and keeps them burning, while also carrying embers and coals that can ignite fires further down the line. 

One just has to think back to the 2017 Knysna and Woodridge/Thornhill fires, where firefighters had to contend with fires that justified the saying “spreads like wildfire”. 

Another unique aspect of veld/bush fires in our region that often catches out-of-towners off guard is when we have beautiful warm-to-hot days as a result of berg wind conditions.

We all know the southwesterly wind will pump through later in the day and cool things down, but could also fuel any fire already burning. 

Many a controlled burn has gone awry by not taking a forecast of such conditions into account. 

One must also bear in mind that the landowner of, especially farms and small holdings, has a lot of responsibility when certain categories are reached, and they would be wise to be fully aware of these regulations.

Some that come to mind are wood cutting, alien vegetation clearing and hikers’ presence on properties when the rating is high.

It is not only for the hikers’ safety, but they can also pose a risk when they make camp fires. 

Even Joe public should not make an open fire for a braai under a dangerous yellow rating.

Finally, please remember that the system is not foolproof and not the beginning and end-all of fire safety.

So be cautious under any category of the FDI, and rather safe than sorry. 

This week in history: 

2012: Port Elizabeth/Gqeberha 

For the umpteenth time in 2012, streets were flooded in one of the wettest years on record. 

Dam levels 

76.48% up from 75.94% last week 

Weather safety tips: 

When undertaking a hike, be it for a day or even longer, check the forecast, and especially the FDI forecast.

You do not want to be caught in the veld/bush in an area you don’t know with a raging fire in the vicinity. 

Now on Facebook, Instagram, and Twitter: WEATHER GURU

E-mail garthsampson59@gmail.com with feedback or requests

HeraldLIVE


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