Fuse Refill Unit

The gasses carry away energy and are part of the proper function of the fuse.

Are you describing a system in which the gasses are used as an indicator to
restore sevice to other unfaulted circuits?

As you said, the gases are carry away energy during fault clearing, but my confusion is the padmounted fuse gear burnt. According to the analysis the gas escaped through the loose threaded connection of the refill fuse unit causes this fire, because of the upstream breaker opened and closed on its reclosure scheme. It opened and closed three times, then since there was a gas build up in the fuse cubicle it ignites fire.

What I thought this gas is not flammable or it should not, so I need some explanation thanks for the reply

'Indoor` fuses are not supposed to produce flamable gas.

The gas produced can be hot enough to ignite a fire if fuel is present.

Was there any fuel in the enclosure? What burned?

These fuses are supposed to be vented to safely handle the gasses.

You state that the unit was loosely threaded. Did you also check that the

vent was free of obstruction to limit pressure? Are you sure it was not

a failure of the unit due to pressure?

Unless the upstream breaker closed very quickly, the fault should have cleared

before power was restored. Look into the coordination of the fuse and breaker.

If the breaker was opening before the fault cleared it may have prevented the

fuse from clearing completely and thus there was a problem when power was

restored to a damaged but not completely cleared fuse.

I appreciate your comment