He works in a mixed environment and is worried about his fast

Mixing
between men and women in the workplace has obvious bad effects on both men
and women. These include the following: 

1 – Haraam
looks. Allaah has commanded the believers, men and women, to lower their
gaze. Allaah, may He be exalted, says (interpretation of the meaning): 

“Tell the
believing men to lower their gaze (from looking at forbidden things), and
protect their private parts (from illegal sexual acts). That is purer for
them. Verily, Allaah is All‑Aware of what they do.

31. And
tell the believing women to lower their gaze (from looking at forbidden
things), and protect their private parts (from illegal sexual acts) and not
to show off their adornment except only that which is apparent”
[al-Noor 24:30, 31]

In Saheeh
Muslim (2159) it is narrated that Jareer ibn ‘Abd-Allaah (may Allaah be
pleased with him) said: I asked the Messenger of Allaah (peace and
blessings of Allaah be upon him) about an accidental glance and he told me
to avert my gaze. 

2 – There
may be haraam touching, which includes shaking hands. The Prophet
(peace and blessings of Allaah be upon him) said: “For one of you to be
struck in the head with an iron needle would be better for him than touching
a woman who is not permissible for him.” Narrated by al-Tabaraani from the
hadeeth of Ma’qil ibn Yasaar; classed as saheeh by al-Albaani in Saheeh
al-Jaami’, no. 5045. 

3 – Mixing
may lead to a man being alone with a woman who is not his mahram, which is
haraam, because the Prophet (peace and blessings of Allaah be upon him)
said: “No man is alone with a woman but the Shaytaan is the third one
present.” Narrated by al-Tirmidhi, 2165; classed as saheeh by al-Albaani in
Saheeh al-Tirmidhi. 

According to
another report: “Whoever believes in Allaah and the Last Day, let him not be
alone with a woman who does not have a mahram with her, for the third one
present will be the Shaytaan.” Narrated by Ahmad and classed as saheeh by
al-Haakim, and al-Dhahabi agreed with him. Also classed as saheeh by
al-Albaani in Ghaayat al-Maraam, 180. 

4 – Another
of its evil results is that a man may become attracted to and infatuated
with a woman, or vice versa, which is as a result of mixing and lengthy
interaction. 

5 – It also
results in destruction of families. How many men have neglected their homes
and families because of being attracted to a colleague at school or at work.
How many women have neglected their husbands and homes, for the same reason.
How many cases of divorce have occurred because of haraam relationships
engaged in by the husband or wife, where mixing at work was the thing that
led to it. 

For these
and other reasons, Islam forbids mixing that can lead to these evil
consequences. We have quoted the evidence for the prohibition on mixing in
detail in the answer to question no.
1200. 

Based on
this, our advice to you is to leave this mixed workplace and look for
another job where you will be free from these haraam things. You should also
be certain that whoever gives up something for the sake of Allaah, Allaah
will compensate him with something better than it, and whoever fears Allaah,
Allaah will grant him a way out from every difficulty. 

“And
whosoever fears Allaah and keeps his duty to Him, He will make a way for him
to get out (from every difficulty).

3. And He
will provide him from (sources) he never could imagine”

[al-Talaaq 65:2-3]

If you have
to stay in this job, then fear Allaah and lower your gaze and do not look at
women. Avoid shaking hands with them or being alone with them, ands remember
that Allaah is always watching. Remember that He knows what is secret and
what is yet more hidden, and He “knows the fraud of the eyes, and all
that the hearts conceal” [Ghaafir 40:19]. 

May Allaah
guide us to fear Him, and to remain chaste and independent of means.

And Allaah
knows best.