Kad je sirena utihnula, vatrogaskinja je rekla da više nema dima.

Because Croatian is using the perfect tense in two different clauses:

• Kad je sirena utihnula = When the siren fell silent
• vatrogaskinja je rekla = the firefighter said

In Croatian, the perfect is usually formed with:

• a form of biti (sam, si, je, smo, ste, su)
• plus the past participle

So here:

• je utihnula
• je rekla

Each clause needs its own verb form.

Utihnula is the past participle of utihnuti, which means to fall silent, to become quiet, or to stop sounding.

Here it agrees with sirena, which is a feminine noun, so the participle is feminine too:

• masculine: utihnuo
• feminine: utihnula
• neuter: utihnulo

So sirena je utihnula literally means the siren became silent.

Because sirena is a feminine noun in Croatian. Most nouns ending in -a are feminine.

That is why the past participle is also feminine:

• sirena je utihnula, not utihnuo

Croatian often shows agreement very clearly, so the verb form tells you the gender of the subject in the past tense.

Because vatrogaskinja is the specifically feminine form meaning female firefighter.

Compare:

• vatrogasac = firefighter (male / sometimes general in older usage)
• vatrogaskinja = female firefighter

Since the sentence uses vatrogaskinja, the later participle also has to be feminine:

• vatrogaskinja je rekla

Rekla is the feminine past participle of reći (to say).

It agrees with vatrogaskinja, which is feminine.

Compare:

• vatrogasac je rekao = the male firefighter said
• vatrogaskinja je rekla = the female firefighter said

So this is another example of past-tense agreement in Croatian.

Kad means when. It introduces a time clause:

• Kad je sirena utihnula = When the siren fell silent

It works much like English when. The whole sentence has the structure:

• When X happened, Y said that Z.

So:

• Kad je sirena utihnula = time/background event
• vatrogaskinja je rekla... = main action

Here da means that and introduces a content clause or reported statement:

• rekla da više nema dima = said that there was no more smoke

This is very common after verbs like:

• reći = to say
• misliti = to think
• znati = to know
• vidjeti = to see

So da connects what was said to the reporting verb.

Because nema requires the genitive case.

Nema is the negative form of ima in the sense of there is / there are / has:

• ima dima = there is smoke
• nema dima = there is no smoke

The noun dim changes to genitive singular dima.

This is a very important Croatian pattern:

• ima vode = there is water
• nema vode = there is no water
• ima vremena = there is time
• nema vremena = there is no time

So dima is there because absence/nonexistence is expressed with nema + genitive.

Here više means any more, no longer, or no more.

So:

• više nema dima = there is no more smoke / there isn’t any smoke anymore

Even though više can also mean more in other contexts, with negation it often has the sense of no longer / not anymore.

For example:

• Ne radim više. = I don’t work anymore.
• Više nema kruha. = There’s no more bread.

So in this sentence, it is not really more in the comparative sense.

Yes. Više nema dima and nema više dima are both natural.

The difference is mostly one of word order and emphasis, not basic meaning.

• više nema dima slightly highlights no longer
• nema više dima may sound a bit more like there is no more smoke

Croatian word order is more flexible than English, especially with short words like je, da, and adverbs like više.

Because Croatian does not need a dummy subject like English there.

English says:

• There is no more smoke

Croatian simply says:

• Nema više dima or Više nema dima

So Croatian often expresses existence or absence without adding an equivalent of English there.

Yes, utihnuti is a perfective verb. It refers to a completed change: the siren became silent.

That matters because the sentence is talking about a finished event:

• the siren was sounding
• then it stopped
• after that, the firefighter spoke

A likely imperfective partner is utihnuti / utihavati or more commonly the idea is contrasted with ongoing sound rather than repeated stopping. In this sentence, perfective is the natural choice because it marks the moment the siren stopped.

Yes, it could come later.

The original order:

• Kad je sirena utihnula, vatrogaskinja je rekla da više nema dima.

You could also say:

• Vatrogaskinja je rekla da više nema dima kad je sirena utihnula.

Putting the kad clause first is very natural because it sets the scene: first the siren stopped, then the statement came.

Croatian is flexible with clause order, though the first version is probably the most neutral here.

Yes, it is fully standard and natural.

It uses several very common features of everyday Croatian:

• perfect tense with je
• kad for when
• da for reported speech
• nema + genitive
• flexible adverb placement with više

So it is a good example of normal Croatian sentence structure.