Learn Russian: При всей опасности расплавленного стекла работа интересна. - For all the danger of the molten glass, the work is interesting.

The preposition при followed by a form of весь (all) in the Prepositional case creates a concessive phrase, meaning 'despite all...' or 'for all...'. Because опасность (danger) is a feminine noun, we use the feminine Prepositional form всей. It is a slightly more formal or emphatic alternative to using несмотря на (despite).

Why does опасность end in -и here?

It is in the Prepositional case, governed by the preposition при. Опасность is a feminine noun ending in a soft sign (a 3rd declension noun). For these nouns, the Prepositional case ending is -и instead of the typical -е used for most other feminine nouns.

What case is расплавленного стекла and why?

It is in the Genitive case. It literally means 'of the molten glass', showing what the danger is associated with. Расплавленного is a past passive participle acting as an adjective here, modifying the neuter noun стекло (glass).

Why is интересна used instead of the full adjective интересная?