Furnace Breakouts

Forensic Services Newsletter

A hole in the side of an electric furnace, after tonnes of molten steel have escaped.

When molten material accidentally escapes from a furnace there are two questions that insurers may put to consultants.

  • What is the cause of the breakout?
  • Was the resulting damage to surrounding equipment as a result of fire?
Steel 1516-1535ºC
Glass 1500ºC*
Cast iron 1177-1232ºC
Copper 1083ºC
Brass 887-1043ºC
Aluminium 660ºC
Zinc 419ºC
*A typical temperature in a glass furnace.  Glass will continue to flow at temperatures down to 1000ºC.

A hole in the side of an electric furnace, after tonnes of molten steel have escaped.

This newsletter addresses the second question. The reason this Molten glass escaping from a glass furnace. question is even asked is because some insurance policies specifically cover damage from breakout, whereas others will only cover damage by fire. Perhaps this could be explained better, but this is a science- based newsletter and insurance distinctions are not our concern.

Since we are only concerned with molten material, it follows that the above were all above their melting points when they broke out, typically of the order of 50ºC higher.

A ladle full of molten steel, with a jammed gate that prevents discharge of the steel in the normal manner. The crane operator has to make an emergency pour into a makeshift pit.

It may seem easy to make the distinction between damage from heat (from the molten material) and damage by fire, but it is not always so. For a start, some molten materials are in a sense themselves burning. Also most items of machinery have coatings that burn, not to mention drive belts, hoses, oil and grease. The difficulty is best explained by pointing out that there is almost always some burning, yet at the same time, we often find that damage is substantially not a result of fire.

Solidified copper after escaping from a furnace. Note how the copper dissolved (alloyed with) the surrounding steel and cast iron, despite the temperature of the molten copper being well below the melting point of either.

Workers holding an oxygen lance during the 'blowing' of an electric furnace melt. Electric furnace steelmaking combines electricity, molten steel, oxygen and water (cooling) in a way that ensures spectacular accidents.

The photograph shows a cross-section through a deteriorated brick, which had even glazed on the furnace side, where arrowed.

Like most technical consulting, this work requires detailed inspection, with observations, notes, measurements and photographs. While familiarity with molten material is of advantage, it is a background in fire investigation that lends itself to this type of work. What is most important is an understanding of fire dynamics and the behaviour of materials when they are heated. A rigorous approach is necessary as conclusions might be challenged by the insured's staff, who have spent their working life heating, smelting, melting and moving molten material from place to place.


Barry Dillon