<p>In this paper, we propose a technique for sizing the width of a firebreak influenced by wind speed and flame burning time. The model used is based on a logistic regression technique, which is trained using data generated by a semi-physical 2D bushfire propagation model. The results of the logistic model were compared with those of an empirical model based on experimental data. The predictions of the model and those from the literature are consistent. The simulations carried out with the model showed, unsurprisingly, that the probability of the fire passing through the firebreak increases with the wind speed and with the burning time of the flames. If the width of the firebreak is twice the length of the flame, the probability of the fire passing through the firebreak exceed 30% when the wind speed is greater than 5&#xa0;m/s and the burning time is greater than 35&#xa0;s. The risk of the firebreak being breached increases rapidly. Consequently, the sizing rule, which takes twice the length of the flame as the width of the firebreak, becomes ineffective when the wind increases and/or the burning time of the flames lengthens. However, simulations have shown that this sizing rule becomes effective when this width is increased by 4&#xa0;m. This result is valid for wind speeds of 10&#xa0;m.s⁻¹ or less. Further studies are required for higher wind speeds, taking into account windblown embers.</p>