If you find yourself in a terror attack similar to the ones that hit Paris last week, do not play dead.

That’s part of the grim new guidance (pdf) being issued by the UK National Counter-Terrorism Security Office (Nactso). The document outlines what to do in “response to a fast-moving incident such as a firearms or weapons attack.”

The advice is based on some evidence from victims of the assault on the Bataclan music hall, the deadliest site of the Paris attacks where gunmen fired indiscriminately at the crowd. Some were able to escape after playing dead among pools of blood.

But Nactso says that ”if you can see the attacker, they may be able to see you.” Instead, the document urges those who find themselves in such an attack to:

Escape if you can.

Consider the safest options.

Is there a safe route? RUN if not HIDE.

Can you get there without exposing yourself to greater danger?

Insist others leave with you.

Leave belongings behind.

For those unable to find a safe route out, the guidance says to find cover from gunfire by hiding behind “substantial brickwork” or “heavy reinforced walls.” The document points out that cover from view does not necessarily mean you are safe as “bullets go through glass, brick, wood, and metal.”

The document also provides guidance on how companies should respond if their buildings becomes the site of a terror attack. Nactso advises companies to train staff in how to lock down buildings, stating:

Dynamic lockdown is the ability to quickly restrict access and egress to a site or building (or part of) through physical measures in response to a threat, either external or internal.

Companies need to also find a way to let people know what’s happening, Nactso says. They could do so by using a dedicated terror alarm, a PA system, existing internal messaging systems (such as text, email, and staff phones), or a “pop-up on employees computers.”

A number of European countries, as well as the US, are under high terror alert following the Paris attacks. Security experts say ISIL may have other attacks in the pipeline.

Read this next: It’s not hypocritical to care more about Paris than Beirut. All our coverage of the Paris attacks can be found here.