U slučaju da vidite požar, pozovite osiguravača.

U slučaju da means in case or if it happens that. In this sentence, it introduces a condition: if you see a fire.

It is similar to ako, but u slučaju da sounds a bit more formal and is very common in instructions, notices, and official language. A more conversational version would be Ako vidite požar, ...

Because the preposition u here requires the locative case. The noun slučaj therefore changes to slučaju.

So:

• slučaj = case, event
• u slučaju = in the event / in case

This is a fixed and very common expression in Serbian.

Here da introduces a subordinate clause: da vidite požar. It does not simply mean English that word-for-word.

In Serbian, da is used in many clause types, and after u slučaju it helps form the meaning in case you see... or if you see... So you should learn u slučaju da + clause as a whole pattern.

Vidite is the 2nd person plural present form of videti (to see). In Serbian, that form can mean either:

• you all see
• you in a polite/formal singular sense

In notices and instructions, Serbian often uses this plural/formal form. An informal singular version would be ako vidiš požar.

Serbian normally uses the present tense after conditional expressions like ako and u slučaju da for future or hypothetical situations. English often does something similar:

• If you see a fire, call...

So vidite is completely natural here, even though the situation may happen in the future.

They both end in -te, but they are not the same kind of form.

• vidite = present tense, you see
• pozovite = imperative, call!

The -te ending often appears with plural or formal singular forms, so the two words look similar. In this sentence, pozovite is an instruction directed at either several people or one person politely/formally.

This is mainly a question of aspect.

• pozvati → pozovite: a perfective verb, suggesting a single complete action, like make the call
• zvati → zovite: more imperfective, which can sound more ongoing or repeated

In instructions like this, Serbian often prefers the perfective imperative because the idea is perform this action once, successfully: call the insurer.

It is in the accusative case as the object of vidite, but for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: požar
• accusative: požar

That is why there is no visible change here.

Because osiguravač is a masculine animate noun, and masculine animate nouns usually take an accusative singular form that matches the genitive singular.

So:

• nominative: osiguravač
• accusative: osiguravača

This is a very important Serbian pattern:

• vidim čoveka = I see the man
• pozovite osiguravača = call the insurer

Yes, the comma is natural here because the sentence begins with a conditional clause: U slučaju da vidite požar, ...

Serbian normally separates that introductory condition from the main clause with a comma. It works much like English:

• If you see a fire, call...

Yes. A few common alternatives are:

• Ako vidite požar, pozovite osiguravača.
  More direct and conversational.

• U slučaju požara, pozovite osiguravača.
  This means in case of fire more generally, without explicitly saying if you see a fire.

The original sentence sounds formal and instruction-like, which fits public notices or official guidance.