The benign type is seen in benign lesions such as benign tumors and following trauma. An aggressive type is seen in malignant tumors, but also in benign lesions with aggressive behavior, such as infections and eosinophilic granuloma.
When setting up a Hookah air system, you will frequently need an array of metal fittings. For use around water, you should use stainless steel or brass fittings only. This is especially important when diving in salt water. Fittings made of ferrous metal will rust or corrode when used in, or near a water environment.
In states like California, which prohibit smoking in bars and restaurants, hookah lounges have to be careful about how they present themselves. Some get around anti-smoking regulations by getting licensed as tobacco shops or cigar clubs, which are allowed to have smoking on their premises.