A segurança vem primeiro.

In Portuguese, abstract nouns are often used with the definite article more often than in English.

So a segurança is very natural for safety or security in a general sense.

• A segurança vem primeiro. = Safety comes first.
• Segurança vem primeiro. is possible in some contexts, but it sounds less standard and less natural as a general statement.

Also, segurança is a feminine noun, so the article is a.

It can mean either, depending on context.

In A segurança vem primeiro, the most common translation is Safety comes first.

But segurança can also mean:

• safety = protection from danger
• security = protection against crime, threats, etc.
• confidence / certainty in some contexts

So the exact meaning depends on the situation. In a workplace, road sign, or general rule, it usually means safety.

Vem is the 3rd person singular form of the verb vir, which means to come.

The subject is a segurança, which is singular, so the verb must also be singular:

• a segurança vem = safety comes

This mirrors the English expression comes first.

A few forms of vir in the present tense:

• eu venho = I come
• você / ele / ela vem = you / he / she comes
• nós viemos = we come
• eles / elas vêm = they come

Notice the difference:

• vem = singular
• vêm = plural

Because primeiro is functioning like first in the expression come first.

Portuguese commonly uses this structure:

• vir primeiro = to come first
• colocar algo em primeiro lugar = to put something in first place

So A segurança vem primeiro is a very natural word order.

A more literal English-style rearrangement would not sound as natural in Portuguese.

Good question. Here, primeiro is not directly describing segurança as an adjective. It works more like an adverbial expression meaning first.

So:

• A segurança vem primeiro. = Safety comes first.

But when primeiro/primeira directly modifies a noun, it agrees in gender:

• a primeira prioridade = the first priority
• o primeiro passo = the first step

In your sentence, primeiro stays in the masculine singular form because it is part of the fixed expression vir primeiro.

Yes. That is also correct and natural.

• A segurança vem primeiro. = Safety comes first.
• A segurança está em primeiro lugar. = Safety is in first place / Safety comes first.

The version with vem primeiro is shorter and more idiomatic as a slogan or principle.

The version with está em primeiro lugar sounds a little more explicit.

A simple pronunciation guide is:

ah seh-goo-RAN-sah vẽy pree-MAY-roh

A few helpful notes:

• segurança has stress on ran: se-gu-RAN-ça
• the ç sounds like s
• vem has a nasal sound, not a full English m
• primeiro has stress on mei

A rough syllable breakdown:

• A
• se-gu-ran-ça
• vem
• pri-mei-ro

Yes, very common.

It is often used to express priorities:

• A família vem primeiro. = Family comes first.
• O respeito vem primeiro. = Respect comes first.
• A saúde vem primeiro. = Health comes first.

So once you learn X vem primeiro, you can reuse it with many nouns.

Yes, it can.

That is another important use of segurança:

• o segurança = the security guard
• um segurança = a security guard

So context matters:

• A segurança vem primeiro. = Safety/Security comes first.
• O segurança vem primeiro. = The security guard comes first.

Notice the article changes too:

• a segurança = safety / security
• o segurança = the guard

It is neutral and very natural in both formal and informal contexts.

You could see it in:

• company policies
• warning signs
• presentations
• everyday speech
• public campaigns

It sounds clear, standard, and idiomatic.

Not if you want the meaning comes first.

• vir primeiro = to come first
• ir primeiro = to go first

So:

• A segurança vem primeiro. = Safety comes first.
• A segurança vai primeiro. would mean something more like Safety goes first, which does not work naturally in this context.

Here are a few natural alternatives:

• A segurança é prioridade. = Safety is a priority.
• A segurança está em primeiro lugar. = Safety is in first place.
• A prioridade é a segurança. = The priority is safety.
• Segurança em primeiro lugar. = Safety first.

The last one, Segurança em primeiro lugar, is especially common on signs, posters, and slogans.

In slogans and signage, yes, Segurança em primeiro lugar is often more common.

Compare:

• A segurança vem primeiro.
  A full sentence. Natural in speech and writing.

• Segurança em primeiro lugar.
  A slogan-style phrase. Very common on posters, safety materials, and notices.

Both are correct. The choice depends on style:

• for a complete spoken statement: A segurança vem primeiro
• for a short motto or sign: Segurança em primeiro lugar