Trevira CS is a man-made yarn used in many fabrics. It is used to make fabrics usually suitable for many contract applications. The constituent yarn is inherently FR Flame / Fire Resistant.
A clear advantage for the contract interior designer is that the FR Flame / Fire Resistance is an industry known and understood property. There are no further complications, risks and costs involved in fire treatment.
However many Trevira fabrics do not meet the Crib 5 standard and further treatment to reach that standard may be required so you must understand the usage and required FR properties.
It is difficult for many FR treatment companies to treat Trevira to pass Crib 5. There are inherent difficulties with the Trevira yarn that cause this. However it is possible to FR treat it to Crib 5. Please contact us for further information.

Re new London * hotel . Please advise periodic cleaning procedures that you recommend for Trevira curtains.
Would hot solvent extraction be suitable and not effect FR
How hot is ‘hot’. Whatever I were to recommend would not be relevant if you had any problems down the line. You should talk to your designer who themselves should provide detailed instruction based on the fabric they have sold you and the FR treatments they organised on your behalf (if any, Trevira is inherently fire retardant).
However to answer your question my personal view would be “Machine washing or dry cleaning will not affect inherent fire retardancy of Trevira”.