Сторож Мерзаметов во время дежурства затопил печь

The watchman Merzametov, while on duty, flooded the stove in the annex to the store and went to a friend living opposite. While he was there (about 3 hours), a fire broke out at the guarded object from a burning log falling out of the furnace. As a result of the fire, material assets worth 300 thousand rubles were destroyed.
Give a criminal law assessment of the actions of Merzametov.

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