Il responsabile della sicurezza chiama il vigile del fuoco.

Here responsabile is being used as a noun, meaning the person in charge, manager, or supervisor.

It can also be an adjective in other sentences, meaning responsible.

A useful thing to know is that responsabile has the same form for masculine and feminine singular:

• il responsabile = the male person in charge
• la responsabile = the female person in charge

So the article tells you the gender, not the ending of the word.

Della is a contraction of di + la.

So:

• di = of
• la = the
• della = of the

Italian often uses di where English uses of or turns a noun into an adjective. So il responsabile della sicurezza literally means the person in charge of the safety, but in natural English it is often something like the safety manager or the person responsible for safety.

Del is a contraction of di + il:

• di = of
• il = the
• del = of the

Vigile del fuoco is a fixed expression meaning firefighter.

Literally, it breaks down as something like guard/watchman of the fire, but you should treat it as a standard job title, not translate it word by word every time.

Because there are two separate singular masculine nouns:

• il responsabile
• il vigile del fuoco

Each noun needs its own article. Italian uses articles very regularly, often more regularly than English does.

So the structure is:

• Il responsabile della sicurezza = the safety manager / the person responsible for safety
• chiama
• il vigile del fuoco = the firefighter

Chiama is the third-person singular present tense of chiamare.

The subject is il responsabile della sicurezza, which is he/she/it in grammatical terms, so the verb must match that subject:

• io chiamo = I call
• tu chiami = you call
• lui/lei chiama = he/she calls

So chiama means calls or is calling, depending on context.

It can mean either one, depending on context.

Italian simple present often covers both:

• he/she calls
• he/she is calling

Without more context, English could translate it in either way.

Yes, Italian word order is somewhat flexible, but Subject + Verb + Object is the most neutral and common order here:

Il responsabile della sicurezza chiama il vigile del fuoco.

You may see other orders for emphasis, but they would usually sound more marked:

• Il vigile del fuoco lo chiama il responsabile della sicurezza would be much less neutral and would need context.
• Chiama il vigile del fuoco il responsabile della sicurezza is possible in certain styles, but not the basic learner-friendly order.

So this sentence uses the most straightforward word order.

Here it is singular: il vigile del fuoco = the firefighter.

The plural is:

• i vigili del fuoco = the firefighters

Notice that vigile changes to vigili, but del fuoco stays the same.

Examples:

• Il vigile del fuoco = the firefighter
• I vigili del fuoco = the firefighters

Yes, the article would change:

• Il responsabile della sicurezza chiama il vigile del fuoco.
• La responsabile della sicurezza chiama il vigile del fuoco.

The noun responsabile itself stays the same in the singular; only the article changes from il to la.

If the firefighter were a woman, Italian often still uses vigile del fuoco as the job title, but article choice may vary depending on usage and context. For a beginner, the main thing to remember is that responsabile does not change form in the singular.

It actually already has one inside della.

Since della = di + la, the noun sicurezza is already being introduced by la:

• della sicurezza = of the safety

So there is no missing article. It is built into the combined form della.

No. Chiamare is broader than English to call in some contexts.

It can mean:

• to call someone on the phone
• to call for someone
• to summon someone
• to name/call someone something in other structures

In this sentence, chiama il vigile del fuoco most naturally means calls/summons the firefighter, and depending on context it may also imply calling by phone.

In this sentence, the role is shown mainly by word order and verb agreement.

• Il responsabile della sicurezza comes before the verb, so it is the subject.
• chiama agrees with that singular subject.
• il vigile del fuoco comes after the verb, so it is the direct object.

So:

• the person in charge of safety = the one doing the action
• the firefighter = the one being called

That is the most natural way to read the sentence.