A safety curtain is a fire safety

Fire safety

Fire safety refers to precautions that are taken to prevent or reduce the likelihood of a fire that may result in death, injury, or property damage, alert those in a structure to the presence of a fire in the event one occurs, better enable those threatened by a fire to survive, or to reduce the...

 precaution used in large proscenium

Proscenium

A proscenium theatre is a theatre space whose primary feature is a large frame or arch , which is located at or near the front of the stage...

 theatres

Theater (structure)

A theater or theatre is a structure where theatrical works or plays are performed or other performances such as musical concerts may be produced. While a theater is not required for performance , a theater serves to define the performance and audience spaces...

. It is usually a heavy fibreglass or iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 curtain located immediately behind the proscenium arch. Asbestos

Asbestos

Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

-based materials were originally used to manufacture the curtain, before the dangers of asbestos were discovered. The safety curtain is sometimes referred to as an iron in British theatres, regardless of the actual construction material.

Occupational safety and health

Occupational safety and health

Occupational safety and health is a cross-disciplinary area concerned with protecting the safety, health and welfare of people engaged in work or employment. The goal of all occupational safety and health programs is to foster a safe work environment...

 regulations state that the safety curtain must be able to resist fire

Fire

Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

 and thereby prevent (or at least hinder) fires starting on stage from spreading to the auditorium

Auditorium

An auditorium is a room built to enable an audience to hear and watch performances at venues such as theatres. For movie theaters, the number of auditoriums is expressed as the number of screens.- Etymology :...

 and the rest of the theatre, reducing injuries to audience members and members of staff.

The curtain is extremely heavy and therefore requires its own dedicated operating mechanisms. In an emergency, the stage manager

Stage management

Stage management is the practice of organizing and coordinating a theatrical production. It encompasses a variety of activities, including organizing the production and coordinating communications between various personnel...

 can usually pull a lever backstage which will cause the curtain to fall rapidly into position.