Flammable vapours caused by a spillage of petrol sparked a boat explosion that injured four adults and two children, fire investigators have said.

Royal Berkshire Fire and Rescue Service (RBFS) have issued a warning to boat owners following the incident, which occurred around midday on 2 August at Bray Lock, in Taplow, near Maidenhead.

The boat was privately owned and there were several adults and children on board at the time of the explosion.

A man and a woman aged in their 40s and a 12-year-old girl who were on the boat were taken to St George’s Hospital in London for treatment.

A woman in her 30s and a three-year-old boy who were also on the boat weretaken to the John Radcliffe Hospital for treatment.

Their injuries are not thought to be life-threatening. Another man was treated at the scene for minor injuries.

Thames Valley Police and RBFS firefighters attended the explosion, which was then investigated by the Marine Accident Investigation Bureau and Environment Agency.

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A spokesman for RBFS said: ‘The boat explosion was caused by a spillage of petrol while the tank was being refuelled.

‘The engine flooded and wouldn’t start and when it did start it ignited the flammable vapours, which caused the explosion.’

Boat owners are advised to follow the fire safety guidance published by RBFS here: http://www.rbfrs.co.uk/pdfs/cs-08-fs-boats.pdf

The Boat Safety Scheme, public safety project owned jointly by Canal & River Trust and the Environment Agency, advises boat owners to exercise extreme caution when refuelling.

Petrol, when spilt or exposed to open air, can quickly vaporise into a low-lying, extremely flammable gas-cloud that can flow into the boat’s interior and pool in the lower parts where any spark could ignite it.

Top tips for refuelling boats with petrol:

1. Use sight, touch and sense of smell to check the fuel system and engine for any petrol leaks or weeping fuel and signs of deterioration, looseness, cracks or any other damage BEFORE starting out and even before the crew boards the boat.
2. Crucially, do not switch on the electrical supply or turn the ignition key if there’s a strong smell of petrol. Ventilate the cabin and bilges and investigate the source.
3. To prevent petrol vapour being blown back or flowing down into the boat during refuelling, close all windows, hatches, doors and awnings; also turn off all cooking appliances and other ignition sources before removing any tank or container caps.
4. Double check before any fuel starts pouring, the correct filling point has been selected. If the worst thing happens and fuel goes down the wrong hole, deal with the situation immediately and get help if you have any issues about handling the problem safely. Warn people around the boat what has happened and what you are doing. Prevent them from igniting the petrol vapour accidentally.
5. Petrol leaks and spills can readily vaporise and ignite in an instant. Clean up any loose fuel straight away and make sure filler caps are secure after refuelling.
6. Avoid decanting petrol from containers, but if you have to, use proprietary anti-spill containers, spouts or nozzles to allow, clean and easy, no-spill refuelling.
7. Avoid refuelling any portable engine or tank aboard the boat; take it to the bank and a safe distance from any boats or other sources of ignition. But always heed any marina or mooring guidance and rules on refuelling and the handling of petrol.
8. If you have to carry spare fuel use proper cans, specifically designed for petrol, anything else could allow fuel and vapours to escape. To comply with UK law, don’t carry more than 30 litres of petrol and ensure that containers are no more than 10 litres if plastic, or 20 litres if metal.
9. Don’t overfill petrol containers, leave some expansion space. Stow them securely upright and protected from pressurisation by siting them away from intense heat and out of direct sunlight. But never stow spare petrol in the engine or cabin space.
10. Never use an open container, such as a bucket, to carry or transfer petrol or mix in 2-stroke oil.

BSS manager, Graham Watts said: ‘With the family standing on the bank and your provisions boxes getting warm in the sun, if you find a leak or there’s a strong smell of petrol, don’t be tempted to start the boat.

‘Open up the windows and hatches and ventilate until the smell has gone away, then investigate. If you can’t fix the problem quickly and easily, pack the boat down and get a competent fitter to put it right so you can enjoy your boat for your next available weekend.’

He added: ‘‘Do not drop your guard, never ignore a strong smell of petrol whilst underway, moor the boat, get everyone off, stop the motor and investigate the cause. Don’t start up again unless you are fully assured that everything is OK and the smell has gone.’

For more information about staying safe from the risk of fire on boats go to www.boatsafetyscheme.org/petrolsafety

As always, prevention is the best cure, as a routine, have a competent marine fitter carry out a thorough service of the engine, fuel system components and controls using the right marine-grade parts when replacements are needed – it could make the difference between a great day out with the family, or swift race to the hospital and no boating for some time afterwards.