An expert died following top-secret explosives tests which were not properly planned and organised, an inquest jury has ruled.
Ministry of Defence scientist Terry Jupp died six days after the accident in August 2002 at the Foulness Island site in Essex.
The 46-year-old suffered between 60 and 90% burns when 10kg of an undisclosed mixture of chemicals suddenly ignited.
It happened during a joint US-UK counter-terrorism project.
The jury at the inquest in Southend, Essex, made a number of criticisms of the experiments in which Mr Jupp, from Hatfield in Hertfordshire, was involved.
They concluded that planning and risk assessment procedures had not been carried out properly, and that a small-scale test involving the potentially dangerous chemicals should first have taken place.
Speaking after the narrative verdict had been delivered, Mr Jupp's widow Pat said listening to the evidence had been "extremely harrowing", but the inquest had been "fair and thorough" and she was "very pleased" with the outcome.
"I think the jury got it right. I don't want anything like this to ever happen again," she said.
"The Ministry of Defence have lost a highly experienced, loyal, dedicated scientist.
"I feel very proud in the knowledge that he helped to save thousands of lives doing the research work that he carried out."
After the inquest, Frances Saunders, chief executive of the MoD's Defence, Science and Technology Laboratory (DSTL), said: "(We) note and acknowledge... the findings of the jury.
"Terry Jupp was carrying out work of national importance, helping to protect the UK, its armed forces and its people and I want to acknowledge publicly his contribution to this vital research.
"Some of the work that DSTL does is, by its very nature, extremely hazardous. But we aim to take every step we can to control and minimise the risks - clearly in this case the measures in place at the time did not safeguard Mr Jupp.
"We take the health and safety of our employees and the public very seriously and since Mr Jupp's tragic death we have done everything we can to prevent such incidents happening again."
The coroner, Peter Dean, had asked jurors to consider a number of questions relating to planning and risk assessment.
One key issue raised at the inquest was whether Mr Jupp knew what chemicals he was mixing at the time of the explosion.
The jury concluded that he did know and had been reassured by risk assessments and his knowledge of explosives.
Mr Jupp was working with a 10kg (22lb) mixture of three substances in a paint container when it unexpectedly ignited.
The jury heard he was engulfed in a fireball, causing horrific injuries from which he never recovered.
A subsequent test involving 27g (less than one ounce) of the mixture produced a violent and sudden ignition, described by one scientist as like a firework going off.
The jury also decided that adequate regard had not been paid to personal protective equipment on the test site, and highlighted communication and organisational problems.
Mr Jupp was involved in tests aimed at combating terrorists in the months following the 9/11 attacks in New York.
Much of the hearing was held in secret to prevent sensitive information falling into the hands of terrorists, and the chemicals involved in the fatal test were referred to only as A, B and C.
One witness said the results could be "catastrophic" if information about the testing fell into the wrong hands.