Answered by Shaykh Yusuf Weltch
Question Summary
Is it permissible to pray sitting or standing throughout the entire prayer if one is in public and cannot find a private space, a clean space, or without disturbing others?
Is it permissible to eat from a place that has a partially halal menu, knowing that cross-contamination is possibly a risk?
Question Answer
In the Name of Allah, the Most Merciful and Compassionate
Praying Sitting or Standing
Standing, bowing, and prostrating are integral parts of the prayer without which the prayer is invalid. That said, some exceptions are made for people physically unable to perform certain actions due to a handicap, sickness, etc… [Tahtawi/Shurunbulali, Hashiyat Maraqi al-Falah]
However, these exceptions are limited to a very small list of legally recognized excuses.
Being in public is not an excuse to leave any of the above integrals of prayer. However, one should aim to find a place off to a side or corner as not to block the way or inconvenience others.
The Sacred Law distinguishes between that which is merely dirty and that which is impure. It is invalid to pray on a place that is impure (i.e., a place that has blood, urine, fecal matter, alcohol, or any of the legally recognized impurities). [Ibid.]
It is unlikely that cannot find anywhere to pray that is free from the above impurities.
That said, it is not permissible to leave the prayer or any of the integrals of the prayer merely because the floor is dirty. One should seek out a clean area (even if it be outdoors) and can even place down a prayer mat or the like as a separation between their body and the ground that may be dirty.
Praying on the Plane
As for praying on the plane and the circumstances that allow one to pray sitting, you can find the answer in this link.
Cross-Contamination
If you are reasonably sure or certain that there is cross-contamination between permitted and forbidden foods, then you must refrain from eating at such an establishment.
If, however, you are doubtful or there merely exists the possibility of cross-contamination, clarify the matter with the establishment by asking them. If they affirm cross-contamination, then you must refrain.
However, if they deny any cross-contamination, you are permitted to eat what is permissible.
What is Considered Cross-Contamination
Cross-contamination is obvious in certain methods of cooking. For example, french fries cooked in the same oil as chicken (non-halal chicken) nuggets which occurs in many fast-food restaurants.
However, other situations are not so obvious. Like, for instance, pizza. It is possible that the knife used to cut a pizza be the same knife used to cut through pepperoni (which can be from non-halal beef or maybe even pork).
The likelihood of this happens is not enough to declare the pizza forbidden (haram) to eat. However, going off the same example, if there are clear traces of the pepperoni on the knife and a visible transference of the pepperoni or its traces on the pizza – then that specific places on the pizza must be avoided.
These are from the advices we heard from our teachers. Apply this principle in other similar situations.
A Note on Caution
Sahl bin S’ad al-Tustari, one of the great early Muslims, said, “Whoever eats of the forbidden (haram) their limbs will disobey them, whether they like it or not or whether they know or not. And whoever’s food is permissible (halal) their limbs with obey them, and they will be guided to all goodness.” [Ghazali, Ihya ‘Ulum al-Din]
From the above, we can see the great importance of only eating of the permissible. This is why caution is pertinent and was highly encouraged by the Prophet (may Allah bless him and give him peace).
The Prophet (may Allah bless him and give him peace) said, “Leave that which gives you doubt for that which does not give you doubt.” [Ahmad]
Summary
Seek out permissible and ideally wholesome food and strive not to eat from places that causes your heart to be unsettled. If you are forced to eat somewhere, apply the above principles. However, try to prevent this by thinking ahead and preparing accordingly.
Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani