kono mondai ha anzen ni kanrensite iru.

は marks 問題 as the topic of the sentence.

So この問題は means something like:

• As for this issue...
• This issue...

In English, we often just start with the subject directly, but Japanese often separates the topic from the rest of the statement.

You could think of the structure as:

• この問題は = as for this issue
• 安全に関連している = is related to safety

問題 can mean several related things depending on context:

• problem
• issue
• question on a test
• matter or concern

In this sentence, issue or problem is probably the most natural translation.

So この問題 is likely:

• this issue
• this problem

If it were talking about homework or an exam, it could also mean this question.

Here, に is the particle required by 関連する / 関連している, which means to be related to.

So the pattern is:

• A は B に関連している
• A is related to B

That means in this sentence:

• この問題は = this issue
• 安全に = to safety
• 関連している = is related

A very important point: 安全に here does not mean safely.

Even though 安全に can sometimes be read as an adverbial expression, in this sentence 安全 is the thing that the issue is related to, and に is the case particle attached to it.

It is functioning like a noun here.

安全 can behave in more than one way:

• as a na-adjective: 安全な場所 = a safe place
• as a noun: 安全 = safety

In this sentence, it means safety, so it is noun-like:

• 安全に関連している = is related to safety

Both are possible, but 関連している is very common when describing an existing state or ongoing relationship.

Compare:

• 関連する = to relate to / to be related to
• 関連している = is related to

In practice, 関連している often sounds more natural when stating that something has a continuing connection.

So this sentence is saying that the issue is in a state of being related to safety.

It comes from the verb 関連する.

Step by step:

• 関連する = to be related to
• 関連して = te-form
• 関連している = te-form + いる

With many verbs, 〜ている can show an ongoing action or a resulting state.
Here it expresses a state:

• 関連している = is related

So it is not really is relating in the English sense. It is more like is connected or is related.

Yes, it sounds fairly formal or written.

This kind of sentence is common in:

• news
• reports
• academic writing
• business contexts
• official explanations

In casual conversation, people might more often say:

• この問題は安全に関係している
• or even more casually, この問題、安全に関係してる

関連している and 関係している are similar, but 関連している often sounds a bit more formal or technical.

They are very close, and both can often be translated as is related to.

A rough distinction:

• 関連している often sounds more formal, objective, or technical
• 関係している is very common and broad in everyday Japanese

For example:

• 安全に関連している = related to safety
• 安全に関係している = related to safety

In many contexts, either would work, but 関連している feels a little more like formal written language.

Japanese word order is somewhat flexible, but this sentence uses a very standard order:

• この問題は = topic
• 安全に = related target
• 関連している = verb phrase

So:

• この問題は安全に関連している

is natural and clear.

You might sometimes see variations for emphasis, but beginners should stick with this pattern:

• A は B に 関連している

Normally it would be written as:

この問題は安全に関連している。

Japanese is not usually written with spaces between words like this.

In speech, depending on the situation, it might sound like:

• この問題は安全に関連している。
  formal
• この問題は安全に関係している。
  a bit more everyday
• この問題、安全に関係してる。
  casual spoken style

At first glance, a learner might think so, because na-adjectives can become adverb-like with に, and 安全に often does mean safely in sentences like:

• 安全に運転する = to drive safely

But in this sentence, that interpretation does not fit the grammar well, because 関連している needs something marked by に to show what it is related to.

So here:

• 安全に = to safety
• not safely

The full structure makes the meaning clear.