Lithium-ion batteries, of the type recalled by Dell, are lighter than their nickel metal hydride predecessors because they enable more power to be packed into a smaller space.

However, to achieve this they often use cobalt oxide, which experts say can undergo a process dubbed "thermal runaway".

That means that once a faulty battery hits a certain temperature – which would differ from model to model – it begins to "self heat", possibly until it catches fire or explodes.

It is not yet known what caused the recent Dell laptop explosions.

Another possibility is that short circuits have been caused by impurities within the battery breaking down the isolator which divides its anode and cathode.

Meanwhile, according to Hewlett Packard, industry standard lithium-Ion notebook PC batteries contain cells that are enclosed environments.

Heat from external sources can make the cells build up pressure. If enough heat is produced (over 105C or 302 Fahrenheit), it can cause the cell release this pressure.

But even less dramatic overheating is bad news for computers and can damage processors, which have a maximum safe internal operating temperature, set by chipmakers.

Intel, the largest chipmaker, defines "typical office room" temperature as 22C (71.6F). Major manufacturers generally regard 35C as the maximum ambient operating temperature.

Anyone working in hotter conditions should monitor their machine’s temperature, experts advise.

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