A considerable number of deaths, major damage to buildings and widespread pollution could have resulted if a chemical site had failed to be made safe.
The dangers were posed at the former Euticals site in Sandycroft after the company went into liquidation.
The shocking scale of the crisis facing Flintshire Council has been laid bare following a Freedom of Information request by the Leader.
It also revealed the local authority has had to fork out more than £3.6 million to deal with the site since 2013.
A council spokesman said the site was predominantly used to process Isosorbide Dinitrate – ISDN – used in the treatment of angina, which in its dry state has similar properties to TNT.
They said: “The ISDN was identified as posing an immediate major off site threat to the local population, which would have a potential impact on approximately 9,000 residents, hundreds of local businesses, environmental damage and pollution of watercourses and air.
”In the event of an explosion the extent of structural damage to buildings and loss of infrastructure was estimated as severe with the assessment of the number of fatalities estimated as considerable.
“A public information zone was imposed at 2.1km to address the increased off site risk on the basis of the high volumes of ISDN; the situation was described as unique.”
In assessing the “off-site” impacts, a number of scenarios leading to major incidents were deemed valid.
They included an on-site fire or explosion quickly spreading throughout the site creating a “noxious plume of toxic gases” and a combined explosion with a force so great that it may have breached the embankment to the River Dee, resulting in significant flooding of the surrounding low lying areas.
It was also deemed possible that pollution from the site could flow into the River Dee, killing fish including devastation of the estuary cockle beds with resulting economic impacts throughout the Dee coast.
The analysis was taken before the company went into liquidation and there were proposals for the company to reduce the amount of chemicals stored on the site.
The spokesman added: “These events were modelled and significant off site scenarios which needed to be managed effectively, but with so much material stored on site the process was slow as the risks presenting themselves were so great.”
Euticals went into liquidation in 2013 and effectively abandoned the Sandycroft site.
The site was passed to The Crown, as is normal protocol, but Flintshire Council “reluctantly” took it on because of the huge public health risk.
Flintshire Council have since had to spend £3,602,399 clearing up the site.
The spokesman said: “The council, with multi-agency support and advice, continued with the site decontamination and de-risking process, a highly complex and time consuming activity due to the presence of explosive material remaining on site and stored in close proximity to other chemicals.
”During the time the site has been in the control of the county council it has been necessary to engage security cover to prevent unauthorised access or removal of items from site and specialist advisors in chemical and explosive material and health and safety, for the reason that the county council had no experience in the management and controlled disposal of explosives/chemicals and substances relating to a dormant and abandoned chemical installation.
“The specialist advisers have provided support and information in connection with the safe and controlled removal of substances on site, necessary safe systems of work and the identification of exactly what was stored externally and where and how this may be safely dealt with.”
The work to remove the explosive material was concluded this month and the council has now managed to offload the site.
The spokesman added: “In November 2014 the council were approached by a company expressing interest in the site. This company is a specialist chemical processing and site remediation business.
“The company wish to expand their operation and have seen this site as an opportunity to deliver their expansion plans and build a business in Flintshire.
“Throughout this period the company has retained its interest in the site.
"The purchaser is taking on significant risks and liabilities with this site, but they have the capability and technical knowledge to remediate the site.
“The site currently remains a risk, financially, reputationally and from a health and safety perspective.
“Disposing of the site transfers this risk to the private sector and to an organisation who have the requisite skills and knowledge to undertake the further final stages of remediation.”
Flintshire Council’s cabinet agreed in February the site – where potentially dangerous chemicals, were left at the base when the company went into liquidation in July 2013 – should be disposed of.
In 2014, Euticals Ltd and previous site operators Archimica Chemicals Ltd were fined a total of £120,000 after workers at the plant suffered life-changing conditions by being exposed to a poisonous gas. Euticals admitted allowing chemicals to escape from the site and failing to notify the authorities when it occurred.
See full story in the Leader