I og med at røgudviklingen er stor, forbliver branddøren lukket.

I og med at is a linking expression meaning something like since, because, or given that.

In this sentence, it introduces the reason:

• I og med at røgudviklingen er stor = Since the smoke production is heavy / Because there is a lot of smoke

It is a bit more formal or written-sounding than everyday fordi. In many contexts, fordi would also be possible, but i og med at can sound slightly more official, explanatory, or technical.

It is best to learn i og med at as a fixed expression.

Word-for-word, it is not very helpful for a learner:

• i = in
• og = and
• med = with
• at = that/to

But together, i og med at functions as a conjunction meaning since / because. So in practice, treat it as one unit.

The part I og med at røgudviklingen er stor is a subordinate clause, and it comes before the main clause.

Danish normally separates this kind of clause with a comma:

• I og med at røgudviklingen er stor, forbliver branddøren lukket.

So the comma marks the boundary between:

1. the reason clause
2. the main statement

This is very common in written Danish.

This is because of normal Danish V2 word order in main clauses.

Danish main clauses usually put the finite verb in the second position. When the sentence begins with a whole subordinate clause, that clause takes the first position. Then the finite verb of the main clause comes next:

• [I og med at røgudviklingen er stor] [forbliver] [branddøren] lukket.

So:

• first position = the subordinate clause
• second position = forbliver
• then comes the subject = branddøren

If you said I og med at røgudviklingen er stor, branddøren forbliver lukket, that would sound wrong in standard Danish word order.

Røgudviklingen is a definite noun meaning the smoke development or more naturally the amount of smoke being produced / the smoke generation.

It is made up of:

• røg = smoke
• udvikling = development
• -en = the definite ending

So:

• røgudvikling = smoke development / smoke production
• røgudviklingen = the smoke development / the smoke production

This kind of compound noun is very common in Danish.

Because it is in the definite singular form: the smoke development.

Danish often puts definiteness at the end of the noun:

• en udvikling = a development
• udviklingen = the development

Since røgudvikling is a common-gender noun (en-word), the definite ending is -en:

• en røgudvikling
• røgudviklingen

So røgudviklingen means the smoke development / the smoke production.

Because røgudviklingen is a common-gender noun, not a neuter noun.

In Danish, adjectives often agree with the noun:

• common gender singular: stor
• neuter singular: stort
• plural/definite uses often: store

Here:

• røgudviklingen is based on en røgudvikling
• so the adjective is stor

That is why you get:

• røgudviklingen er stor

If it were a neuter noun, you would expect stort instead.

Forbliver means remains or stays.

It comes from the verb at forblive = to remain.

So:

• branddøren forbliver lukket = the fire door remains closed

It is used here because the sentence describes a continuing state, not an action of closing:

• forbliver lukket = stays closed
• not becomes closed
• not is being closed

This fits the context well: because there is a lot of smoke, the fire door stays shut.

Here, lukket is functioning like an adjective meaning closed.

So:

• branddøren forbliver lukket = the fire door remains closed

This describes the state of the door.

Compare:

• Døren er lukket = The door is closed
• Døren lukkes = The door is being closed / The door gets closed

So lukket focuses on the result or state, while lukkes would describe an action or passive process.

Branddøren means the fire door.

It is another compound noun:

• brand = fire
• dør = door
• -en = the definite ending

So:

• en branddør = a fire door
• branddøren = the fire door

Again, Danish very often builds longer nouns by joining smaller words together.

Because it is definite singular: the fire door.

The base noun is:

• en dør = a door

In a compound:

• en branddør = a fire door
• branddøren = the fire door

The definite ending goes on the whole compound noun, not on the first part.

Yes, very often it could.

For example:

• Fordi røgudviklingen er stor, forbliver branddøren lukket.

That would also mean Because the smoke production is heavy, the fire door remains closed.

The difference is mainly one of tone and style:

• fordi = very common, neutral, everyday
• i og med at = somewhat more formal, explanatory, or official-sounding

In technical or safety-related language, i og med at can sound quite natural.

Yes, it is natural enough in Danish, especially in technical, official, or safety-related language.

A more literal English translation like the smoke development is large sounds odd in everyday English, but in Danish røgudvikling is a normal way to talk about how much smoke is being produced.

So this is a good example of where the Danish wording is natural, even if the most natural English translation uses a different structure, such as:

• there is a lot of smoke
• smoke production is heavy
• the amount of smoke is high

It sounds fairly formal, technical, or instructional.

Clues include:

• i og med at instead of simpler fordi
• compound nouns like røgudviklingen and branddøren
• the verb forbliver, which is slightly more formal than very everyday phrasing

This is the kind of sentence you might see in:

• safety instructions
• building regulations
• technical documentation
• emergency procedures

Yes. A helpful breakdown is:

• I og med at = since / because
• røgudviklingen = the smoke production
• er stor = is large / is heavy
• forbliver = remains
• branddøren = the fire door
• lukket = closed

Structure:

• Reason clause: I og med at røgudviklingen er stor
• Main clause: forbliver branddøren lukket

That makes it easier to see both the meaning and the word order.