In 1999 the International Electrotechnical Commission (IEC) began development of a standard for the electrostatic classification of flexible intermediate bulk containers (FIBC). Pail of this effort addressed gas ignition testing for FIBC used in flammable atmospheres, drawing on test procedures used by various test laboratories. Critical examination of IECs 2003 working draft raised a number of technical issues requiting experimental resolution. This article describes research and development leading to publication of IEC 613404-4:2005, It is shown that some FIBC previously regarded as "Type D" fail the new IEC standard test because factors such as charging current and test gas ignition energy were formerly not standardized at appropriate values. (c) 2005 American Institute of Chemical Engineers Process.