More than half of the Bangladesh garment factories that do work for a group of North American retailers and apparel makers have already been inspected for fire and building safety, the group said on Tuesday.

Last week, the Alliance for Bangladesh Worker Safety released a list of more than 620 factories its 23 current members do business with.

Bangladesh garment factory working conditions have been under close scrutiny since the April collapse of the Rana Plaza factory complex killed more than 1,100 garment workers and a November 2012 fire at the Tazreen factory killed 112 workers.

Members of the Alliance, including industry heavyweights such as Gap, VF Corp and Wal-Mart Stores, have agreed to inspect all of the Bangladesh factories from which they source goods within a year. So far, more than 50 percent of those factories have been inspected. It was not immediately clear how many factories may or may not need to make safety improvements based on those inspections.

The Alliance said it plans to have experts review and assess those inspections. If any inspection does not meet its requirements, another inspection will have to be completed.

About 3.6 million people work in Bangladesh's clothing industry, making it the world's second-largest clothing exporter behind China. Some of the mostly female workforce earn as little as $38 (23.40 pounds) a month, and workers are pushing for an increase in the minimum wage. About 60 percent of garment exports go to Europe and 23 percent to the United States.

Roughly 50 percent of the factories that do business with members of the Alliance also make garments for members of the separate European-led Accord and Fire and Building Safety.

The Accord group, which had 100 companies on board as of this month, is doing its own work to ensure the safety of garment workers in Bangladesh. Accord members include U.S. companies such as Abercrombie & Fitch and American Eagle Outfitters Inc.

The Alliance also said that it has appointed two technical experts to help implement its fire and building safety standards and inspection process, adhering to a set of fire and building safety standards that it says align with the Bangladesh National Building Code. The people assigned to that task are Dr. Ishtaique Ahmed, a professor of civil engineering at the Bangladesh University of Engineering; and Technology and Tracey Bellamy, chief engineering officer for Telgian Corp, a fire protection and safety services firm, the Alliance said.