После тревоги мы долго обсуждали инструкцию и план эвакуации.

Because после (after) requires the genitive case.

• Dictionary form: тревога
• After после: после тревоги

So тревоги is the genitive singular form of тревога.

This is a very common pattern in Russian:

• после урока = after the lesson
• после работы = after work
• после тревоги = after the alarm / alert

После takes the genitive case.

So any noun after после must be in the genitive:

• после тревоги
• после собрания
• после обеда

This is something learners usually just memorize as part of the preposition:
после + genitive

Yes, Russian can often omit subject pronouns when the verb already makes the subject clear. So both are possible:

• Мы долго обсуждали инструкцию и план эвакуации.
• Долго обсуждали инструкцию и план эвакуации.

Including мы makes the subject explicit. It can add clarity, contrast, or simply sound natural in context. In this sentence, мы is not strictly required, but it is perfectly normal.

Because the subject is мы (we), and in the past tense Russian verbs agree in number (and in the singular, also gender).

Past tense forms of обсуждать:

• обсуждал = he was discussing / discussed
• обсуждала = she was discussing / discussed
• обсуждало = it was discussing / discussed
• обсуждали = they / we were discussing / discussed

Since the subject is мы, the correct form is обсуждали.

This is about aspect.

• обсуждали = imperfective
• обсудили = perfective

In this sentence, обсуждали fits well because the focus is on the process or duration of the discussion, especially with долго (for a long time).

• Мы долго обсуждали... = We spent a long time discussing...
• Мы обсудили... = We discussed / went over it and finished

So долго strongly encourages the imperfective here, because it emphasizes how long the action lasted.

Долго is an adverb, and here it means for a long time or for long.

It modifies the verb обсуждали:

• долго обсуждали = discussed for a long time

Russian adverbs do not change form for case, gender, or number.

Compare:

• долго ждали = waited a long time
• долго говорили = talked for a long time
• долго обсуждали = discussed for a long time

Because it is a direct object, so it takes the accusative case.

The dictionary form is:

• инструкция = instruction / manual / set of instructions

Its accusative singular form is:

• инструкцию

So:

• обсуждали инструкцию = discussed the instruction / the manual / the instructions

This is a normal pattern for feminine nouns ending in -а / -я:

• книга → книгу
• машина → машину
• инструкция → инструкцию

Because план is the main noun, while эвакуации depends on it.

• план = plan
• эвакуация = evacuation

In Russian, plan of evacuation is expressed as:

• план эвакуации

This uses the common pattern:

noun + noun in the genitive

So:

• план stays in the accusative singular, but for masculine inanimate nouns like this, accusative = nominative
• эвакуации is genitive singular of эвакуация

Similar examples:

• план города = map/plan of the city
• центр Москвы = center of Moscow
• начало урока = beginning of the lesson

It is two coordinated direct objects joined by и (and):

• инструкцию
• план эвакуации

Both are things that we discussed.

So the structure is basically:

• обсуждали что?
  • инструкцию
  • и план эвакуации

This is just like English:
discussed the instructions and the evacuation plan

Because Russian has no articles like English a/an/the.

So:

• инструкция can mean an instruction, the instruction, or sometimes instructions
• план эвакуации can mean an evacuation plan or the evacuation plan

The exact meaning depends on context.

In this sentence, context probably makes them definite in English, so translation often uses the:

• the instructions
• the evacuation plan

But Russian itself does not have separate article words.

Yes. Russian word order is relatively flexible because case endings show the grammatical roles.

The given order is neutral and natural:

• После тревоги мы долго обсуждали инструкцию и план эвакуации.

But other orders are possible, for example:

• Мы после тревоги долго обсуждали инструкцию и план эвакуации.
• Инструкцию и план эвакуации мы долго обсуждали после тревоги.

These versions may sound slightly different in emphasis, but the basic meaning stays the same.

Very roughly:

• earlier in the sentence = often background or topic
• later in the sentence = often more emphasis or new information

Not usually in this sentence.

Тревога can mean:

1. anxiety / worry
2. alarm / alert

In the phrase после тревоги, especially with инструкция and план эвакуации, it most likely means:

• after the alarm
• after the alert
• possibly after the emergency alarm

So here it is probably not emotional anxiety, but an actual alarm or emergency signal.

It is genitive singular.

Dictionary form:

• эвакуация = evacuation

Form in the sentence:

• эвакуации = of evacuation

So план эвакуации literally means plan of evacuation, not plan of evacuations.

In neutral speech, the sentence might be read with natural stress on the content words:

После тревоги мы долго обсуждали инструкцию и план эвакуации.

Depending on context, different words can be emphasized:

• ПОСЛЕ тревоги... if contrasting with before the alarm
• мы if contrasting with another group
• долго if emphasizing the length of time
• инструкцию и план эвакуации if emphasizing what was discussed

So the sentence is grammatically fixed, but spoken emphasis can shift the focus.

Yes, both can be possible depending on context.

Because Russian aspect and tense do not match English tenses one-to-one, обсуждали may correspond to:

• were discussing
• discussed
• used to discuss in other contexts

In this sentence, the most natural English translation is usually:

• After the alarm, we discussed the instructions and the evacuation plan for a long time.

or

• After the alarm, we were discussing the instructions and the evacuation plan for a long time.

The first is more natural in ordinary English, even though the Russian verb is imperfective.