POISONOUS levels of carbon dioxide are preventing Hampshire fire fighters from assessing damage to a blaze-hit car carrier carrying millions of pounds of cargo.

For two days more than 40 fire fighters from across Southampton have been based at Berth 38 keeping a watchful eye on the US-registered Courage.

Its crew was able to use a special in-built CO2 flooding system to suppress the flames and it is thought the fire is out.

But high levels of “poisonous” carbon dioxide remain on the ship meaning fire fighters are unable to confirm this.

It is not expected that an analysis of how much damage has been caused will begin until later today (Saturday).

The blaze broke out shortly before 10pm on Tuesday night when the vessel was 40 miles off the Essex coast.

It was described as ‘severe’ and is understood to have spread across four decks.

Although Hampshire Fire and Rescue marine response officers were winched on board earlier in the week to confirm the fire was out, regular fire crews have been unable to access the damaged deck due to the residual heat that was trapped inside the compartment.

A spokesman for Hampshire Fire and Rescue Service said: “The merchant vessel Courage continued to be monitored throughout the night and remained cool with no signs of fire.”

Now fire fighters are beginning the laborious process of “safely ventilating” the parts of the ship which have been affected by the blaze.

The spokesman added: “A tactical plan has now been agreed between Hampshire Fire and Rescue Service, the ship’s captain, the Harbour Master and the Maritime and Coastguard Agency.

“In preparation for the opening of the affected compartment, the on-board CO2 system that was used in the initial stages of the fire has now been recharged.

“The amount of CO2 that was released into the ship has meant the assessment and the tactical plan going forward have had to be managed in a controlled manner, as many parts of boat have high levels of CO2 that require crews to wear breathing apparatus.

“Upon confirmation that the fire is fully out, a staged plan to ventilate the compartment and the affected areas of the vessel will be carried out.”

It is possible that around 100 new and used vehicles could have been in the part of cargo hold which caught fire.

Courage is owned by American Roll-On Roll-Off Carriers (ARC) who confirmed the ship’s crew of 24 were all unharmed.

A spokesman from ARC was unable to confirm what cargo was stored in the affected areas.

The vessel weighs 52,000 tonnes and had been carrying a mix of new and used commercial vehicles and some vehicles and furniture belonging to US military personnel.

It was bound for Southampton from Bremerhaven in Germany.