Cross over

I have been hugely enjoying the Netflix real life documentary series, The Big Timber, which follows the vicissitudes of a timber mill located on Vancouver island.

I was particularly interested in the revelations that timber felling and Forest operations are strictly regulated and that in the summer forest operations must stop when the so-called ‘crossover point’ has been reached.

This is when the relative humidity and the temperature are the same and it is surpassed when the relative humidity is lower than the temperature. At the crossover point it is considered that forestry waste, brash etc reaches an extremely flammable situation (it becomes tinder dry) and that should a fire occur at or below/above (?) the crossover point that fire will be almost impossible to extinguish and spread dramatically.

In our woods here I am not aware of them using a crossover point as the signal for the prohibition of forestry operations. Rather tree felling is prohibited after spring time (15th April) dependent on altitude and the clearance of felled wood has to be completed 30 days later(in Piedmont at least and again dependent on altitude . I can’t find the Tuscan dates.)

The photo here is of my little weather station’s display. At 14.46 today the outside temperature was 35.4C with relative humidity of 39%. If that relative humidity stood at 35% the crossover point would have been reached.

You can also see that the internal temperature in our bedroom was 27.7C at the same time with, as is usually the case, a high relative humidity (53%) than that prevailing outside. This data shows the crossover point inside was a long way off and the chances of either of us spontaneously combusting was consequently medium to low.

Breaking: the crossover point was reached here at 15:21 when RH was 36% and temp was 36C (see extra).

Link to fire risk Kestrel monitor he was using on Big Timber - looks like fab kit for outdoorsy guys who have everything https://kestrelmeters.com/products/kestrel-3550fw-fire-weather-meter