The Health and Safety Executive (HSE) prosecuted BAE Systems Land Systems (Munitions and Ordnance) Ltd following Lynda Wilkins' death at the company's explosives plant on Central Avenue in Chorley.
Liverpool Crown Court heard that Mrs Wilkins was working with lead styphnate, a sensitive primary explosive, on 2 March 2005 when she was killed. HSE has been unable to establish the exact cause of the explosion as Mrs Wilkins was working alone.
The HSE investigation found that the company allowed unsafe working procedures to develop by providing too little supervision and monitoring.
BAE Systems, of Farnborough Aerospace Centre in Hampshire, pleaded guilty to breaching Section 2(1) of the Health and Safety at Work etc Act 1974 by failing to ensure the safety of its employees.
It was ordered to pay GBP£118,000 towards the cost of the prosecution, in addition to the fine, at Liverpool Crown Court on 14 January 2010.
HSE Inspector Colin Hutchinson said:
'This was a tragic incident and my sympathies go to Lynda Wilkins' family. Although we have been unable to conclude what caused the explosion, it is clear that BAE Systems' failings contributed to her death.
'The substance she was using is known to be extremely sensitive and must be handled carefully. BAE Systems failed to ensure the process was properly supervised and monitored.
'Explosives companies must learn from this incident by making sure their safety procedures are both sufficient and rigidly followed to avoid needless loss of life in the future.'