The aim of this paper is to provide new experimental data on the minimum ignition energy (MIE) of clouds of fibres dispersed in the air. Nylon fibres from an Italian flock manufacturer (diameter between 10 and 27.4 mu m, length between 600 and 1800 mu m) were collected and tested in a modified Hartmann tube in order to measure the MIE. The instrument is equipped with a capacitive triggering system. The ignition energy ranged between 4 mJ and 4J, and the delay time between dispersion and ignition could be set at a range between 30 and 180 ms. Two levels of energy were identified, named E(1) and E(2), for each fibre dimension, according to Cesana and Siwek [2001. Operating Instructions for the Mike 3 Minimum Ignition Energy, Adolf Kuhner AG, Switzerland ASTM Committee E-27.05 (2001)] and ASTM [2002. E 2019-99 Standard Test Method for minimum Ignition Energy of a Dust Could in air, Annual Book of ASTM Standards 2002 (pp. 769-776). USA: ASTM International.]. E(2) is the lowest energy value at which ignition occurs at least once in ten successive tests, and E(1) is the highest energy value at which no ignition is observed in at least ten successive tests. A third energy level, named E(3), was identified as the value at which explosion occurred in five consecutive tests. The probability of ignition between E(1) and E(3) was measured as a function of the spark energy at a given fibre concentration. The influence of the diameter and of the length of the fibres on the MIE was observed separately. (C) 2008 Elsevier Ltd. All rights reserved.