Brandsikkerheden er vigtig i hele bygningen.

Because Danish normally writes noun compounds as one word.

So:

• brand = fire
• sikkerhed = safety
• brandsikkerhed = fire safety

English often separates these ideas into two words, but Danish usually joins them. This is very common in Danish, especially with nouns.

You can split it into three parts:

• brand = fire
• sikkerhed = safety
• -en = the definite singular ending

So brandsikkerheden literally means the fire safety.

A useful rule: in Danish compounds, the last part is the main noun. Here the main noun is sikkerhed, so the whole word behaves like sikkerhed.

Because Danish often puts the definite article at the end of the noun instead of using a separate word like English the.

Compare:

• en brandsikkerhed = a fire safety measure / a fire safety concept
• brandsikkerheden = the fire safety

The noun sikkerhed is a common-gender noun, so its definite singular ending is -en.

Er is the present tense of at være, meaning to be.

So:

• er = is / are

In this sentence, it links the subject brandsikkerheden with the description vigtig:

• Brandsikkerheden er vigtig = Fire safety is important

This is the normal Danish way to make a sentence like X is important.

Because the adjective agrees with the noun it refers to.

Here the subject is brandsikkerheden, and the head noun is sikkerhed, which is common gender and singular. For a common-gender singular noun, the adjective usually appears in its basic form:

• vigtig = important

Compare:

• Bogen er vigtig = The book is important
• Huset er vigtigt = The house is important

So vigtigt would be used with a neuter singular noun, not with brandsikkerheden.

Hele means whole, entire, or all of.

So:

• i hele bygningen = in the whole building / throughout the building

In natural English, this is often best understood as throughout the building.

Because hel changes form depending on what kind of noun it modifies.

The main forms are:

• hel for common-gender singular indefinite: en hel bygning
• helt for neuter singular indefinite: et helt hus
• hele for plural or definite nouns: hele bygningen, hele husene

Since bygningen is definite singular, hele is the correct form.

That is a very good question, because Danish often uses double definiteness with adjectives:

• den store bygning = the big building

But some words, including hele, often do not take that extra den. So Danish says:

• hele bygningen = the whole building

not normally:

• den hele bygning

So this is a pattern worth learning as a set phrase:

• hele bygningen
• hele huset
• hele dagen

Because bygningen is the definite singular form of bygning.

• bygning = building
• bygningen = the building

The sentence is talking about a specific building, not just any building, so the definite form is used.

Because i is the normal preposition for something happening inside or throughout the inside of a building.

So:

• i bygningen = in the building
• i hele bygningen = throughout the building

På bygningen would usually suggest on the building or on its surface, which is not the meaning here.

Yes. Danish often allows another element to come first, but the verb still stays in second position.

For example, you could also say:

• I hele bygningen er brandsikkerheden vigtig.

That still means roughly the same thing, but now the location phrase is emphasized first.

This is a key Danish rule called V2 word order:

• one element first
• the finite verb second

So both are possible, but the original sentence is the most neutral and straightforward version.