HRC fuses

This doesn't sound right.

Internally, an HRC fuse is simply made of silver wires and silica sand, hermetically sealed to prevent explosion in the event of a high current fault.

There have been some cases where low voltage HRC fuses have exploded under high fault conditions, but I am not aware of this occurring simply by heating an HRC fuse.

Where did you hear about them exploding in a fire or at high heat?

HRC fuses use copper-shim or wire, not Silver. Silver is used only in Semiconductor-Fuses Marked as "R". These are very rapid blowing & are only short-circuit protection rather than over-load-protection.

Not always ""hermetically sealed "". Fuses with simple blown-indicators are not

I have never seen a HRC fuse explode when subjected to high heat or fire. Are you sure of such?

When a HRC fuse carrys normal rated current, the temperature of the fuse element dose not reach melting point. At the occurrance of a short circuit fault, short circuit current flows through the fuse element and the element melts before the fault current reaches its first peak. As heat is produced the melted fuse element vaporizes. The chemical reaction between silver vapour and filling powder tends to establish high resistance. This high resistance acts as an insulator because the fault current decreases along with the high pressure created within the fuse by the fault current. After which a transient voltage is created at the instant of fault current interruption on account of sudden release of energy.

With that I don't think a HRC fuse will explode as in a bumb when exposed to high heat o fire.

I have heard of a case where the fuse had been in water and then placed in a UPS. The fuse exploded when the capacity was exceeded and the water turned to steam.

Don't try this it at home!

Such cases are not due to manufacture defect but carelessness of the concerned personnel.

And the fuse was not sure an hermetically sealed