Brannskaden og nedkjølingen er farlige.

In Norwegian, the definite article is usually attached to the end of the noun instead of standing as a separate word.

• en brannskade = a burn injury

• brannskaden = the burn injury

• en nedkjøling = a cooling / hypothermia
• nedkjølingen = the cooling / hypothermia

So -en here marks the nouns as definite.

Because Norwegian usually puts definiteness on the noun itself.

Compare:

• a burn injury → en brannskade
• the burn injury → brannskaden

This is one of the biggest differences from English. Instead of using a separate article like the, Norwegian often uses a suffix such as -en, -et, or -a.

Because the subject is plural in meaning: it consists of two things joined by og (and):

• brannskaden
• nedkjølingen

Together, they form a plural subject, so the adjective must be plural too:

• singular: farlig
• plural / definite adjective form: farlige

So:

• Brannskaden er farlig. = one thing is dangerous
• Brannskaden og nedkjølingen er farlige. = two things are dangerous

Because er is the present tense of å være (to be), and it does not change for singular vs. plural.

So Norwegian says:

• jeg er
• du er
• han er
• vi er
• de er

Unlike English, Norwegian does not have is/are/am distinctions in the present tense. It is always er.

Each noun is singular by itself:

• brannskaden = the burn injury
• nedkjølingen = the cooling / hypothermia

But when they are joined with og, the whole subject becomes plural:

• X og Y er farlige = X and Y are dangerous

So the nouns themselves are singular, but the combined subject is plural.

Yes. Norwegian very often combines nouns into one word.

• brann = fire / burn
• skade = injury / damage
• brannskade = burn injury

This is very normal in Norwegian. English often uses two words where Norwegian uses one compound word.

Literally, nedkjøling means cooling down or lowering of body temperature. In medical or emergency contexts, it can refer to hypothermia or dangerous loss of body heat.

So the exact English translation depends on context, but grammatically it is a noun formed from the verb å kjøle ned (to cool down).

Yes, that can be possible in some contexts, but it changes the feel.

• Brannskaden og nedkjølingen er farlige points to specific things, or to those conditions as identifiable items in context.
• Brannskade og nedkjøling er farlig is more general, like talking about those phenomena in general.

Also note the adjective difference:

• when treated as a general combined idea, you may sometimes see farlig
• when clearly referring to two separate items, farlige is the natural choice

For a learner, the safest reading of your sentence is: two definite nouns joined by og, therefore farlige.

The sentence follows standard Norwegian word order:

Subject + verb + adjective

• Brannskaden og nedkjølingen = subject
• er = verb
• farlige = subject complement / adjective

This is very similar to English word order in a simple statement.

Both brannskade and nedkjøling are normally treated as common-gender nouns in Bokmål, so they take en in the indefinite singular:

• en brannskade
• en nedkjøling

That is why their definite singular forms are:

• brannskaden
• nedkjølingen

It is based on the verb å kjøle ned (to cool down).

A simplified breakdown is:

• kjøl = related to cooling
• ned- = down
• -ing = a noun-forming ending, similar to English -ing in some cases
• -en = definite ending

So nedkjølingen is basically the cooling down / the hypothermia.

A few things may be tricky for English speakers:

• kj in nedkjølingen is a soft sound that does not exist in standard English
• ø is a vowel English does not have
• brannskaden has a consonant cluster that may feel heavy at first

You do not need perfect pronunciation immediately, but kjø is especially worth practicing because it is a very common Norwegian sound pattern.