Learn Hardcore French: Une voisine descend l'escalier de secours sans paniquer. - A neighbor goes down the emergency staircase without panicking.

une voisine = a neighbor (no specific one, just some neighbor)
la voisine = the neighbor (a specific neighbor, already known in the context)

In the sentence, we are just introducing some neighbor who is going down the fire escape, so French uses the indefinite article (une). If the context had already identified her, then la voisine would be more likely.

Why is it descend and not something like est en train de descendre?

French simple present (elle descend) often covers both:

English she goes down
English she is going down

So Une voisine descend l’escalier de secours can be understood as:

A neighbor is going down the fire escape (action in progress)
or
A neighbor goes down the fire escape (more neutral present)

Être en train de + infinitive (like est en train de descendre) also exists, but it’s used when you really want to insist on the action being in progress right now. In many cases, French just uses the simple present where English uses the -ing form.

Why does descendre not use an auxiliary verb here, like elle a descendé or something?

The sentence is in the present tense, not the past, so no auxiliary is needed:

elle descend = she goes down / she is going down (present)
elle est descendue = she went down / she has gone down (past, intransitive)
elle a descendu l’escalier = she went down the stairs / she brought the stairs down (past, transitive)

Here, descendre is in the simple present: descend is just the 3rd person singular of descendre (je descends, tu descends, il/elle/on descend, etc.).

Why is it l’escalier and not le escalier?

Escalier is masculine, so the basic form is le escalier (the staircase).
However, French uses elision: when le comes before a word that starts with a vowel or a mute h, le becomes l’:

le ami → l’ami
le escalier → l’escalier

The pronunciation is smoother: l’escalier.

What exactly does escalier de secours mean? Is it always “fire escape”?

Literally:

escalier = staircase, stairs
de secours = of emergency / for rescue

So escalier de secours is a staircase intended for emergency use. In most building contexts, that corresponds to:

English fire escape (especially the external metal stairs on a building)
more generally: emergency staircase / emergency exit stairs

You’ll see de secours in other phrases too:

sortie de secours = emergency exit
numéro de secours = emergency number

Why is there de in escalier de secours and not something like escalier secours?

In French, when one noun modifies another (like “fire escape” in English: noun + noun), the common pattern is:

[main noun] + de + [second noun]

So:

escalier de secours (literally: stair of emergency)
verre d’eau = glass of water
sac de sport = sports bag

English often uses noun + noun (“fire escape”), but French usually needs de to link them.

What does sans paniquer literally mean, and why is paniquer in the infinitive?

sans = without
paniquer = to panic (infinitive)

So sans paniquer = without panicking.

French often uses sans + infinitive where English uses without + -ing:

sans manger = without eating
sans parler = without speaking
sans paniquer = without panicking

You don’t conjugate the verb after sans here; you keep it in the infinitive.

Could we say sans panique instead of sans paniquer?

You could say sans panique, but:

sans paniquer emphasizes the action/state (she does not panic, she keeps calm while doing it).
sans panique emphasizes the absence of panic as a thing (there is no panic present).

In this context, sans paniquer is more natural, because we are describing how she descends (she does it without panicking).

Where could we put sans paniquer in the sentence? Is its position fixed?

The position is flexible. All of these are grammatically correct, with slightly different focus:

Une voisine descend l’escalier de secours sans paniquer.
– Neutral, “without panicking” just describes the manner.
Sans paniquer, une voisine descend l’escalier de secours.
– Emphasizes her calmness first.
Une voisine, sans paniquer, descend l’escalier de secours.
– Adds sans paniquer as a sort of side remark; slightly more literary or written style.

All keep the same basic meaning.

How would the sentence change if the neighbor were male?

You would change only the subject:

Un voisin descend l’escalier de secours sans paniquer.

Changes:

une voisine → un voisin
The verb descend stays the same (3rd person singular is identical for masculine and feminine subjects).
The rest of the sentence is unchanged.