Evacuate, Invacuate or Lock Down? Why “Just Get Everyone Out” Can Be the Wrong Response

For most of our working lives, we've been taught a very simple response to an emergency.

The alarm sounds.

Get everyone out.

For a fire, that principle is well understood. Staff know the exits, people leave the building and everybody moves away from the danger.

But what happens when the danger is outside?

What if a terrorist attack is taking place immediately outside your main entrance?

What if the normal evacuation route takes people towards an attacker?

What if your designated assembly point is closer to the threat than the building you're evacuating?

Or what if moving hundreds of people at once actually creates a greater risk than keeping some of them exactly where they are?

I've worked in policing and private security for more than two decades, and this is an area I've thought about for a long time.

For me, the question during a hostile incident shouldn't automatically be:

“How do we get everyone out?”

It should be:

“Where is the danger, and where are our people safer?”

That difference matters.

What is the difference between evacuation, invacuation and lockdown?

In simple terms:

Evacuation means moving people away from danger by getting them out of all or part of the premises or event.

Invacuation means moving people away from danger to a safer location within the premises or event. This can include bringing people inside from outside or moving them from one part of a building to another.

Lockdown means securing all or part of a premises or event to prevent or restrict people entering or leaving.

There is also a fourth element that I think is every bit as important:

Communication.

People need to know there is a danger and what they are expected to do.

These aren't simply terms used within the security industry. Evacuation, invacuation, lockdown and communication are the four public-protection procedures identified within current UK statutory guidance under the Terrorism (Protection of Premises) Act 2025, commonly referred to as Martyn's Law.

But knowing the definitions isn't enough.

The important part is understanding when each response might be appropriate.

Why might a normal fire evacuation be dangerous during a terrorist attack?

Fire has conditioned us to think about moving people outside.

And rightly so.

If the building is on fire, getting people away from the fire is generally the objective.

A hostile attack can be completely different.

Imagine there is an attacker immediately outside your building.

Your normal fire alarm activates.

Hundreds of people respond exactly as they've been trained to respond and start leaving through their normal exits.

You could potentially be sending them directly towards the threat.

Current statutory guidance specifically recognises this difference. It says organisations should consider whether an attack is taking place inside or outside the premises and warns that terrorist-attack evacuation procedures should, where possible, avoid relying on the normal fire alarm because people may respond inappropriately to the threat.

That's why I believe emergency planning needs to go considerably further than:

“Here are the fire exits.”

The Borough Market attack changed the way I approached this

Following the Borough Market terrorist attack, I worked with a client to review what we would actually do if something similar happened near their venue.

It was a busy location with significant numbers of customers.

The obvious terminology would have been invacuation.

But I had a problem with writing a procedure that simply said:

“Invacuate all customers.”

Because I didn't believe we could.

Not realistically.

We had to consider the number of people in the venue, the layout of the building, available internal areas, how quickly information might reach us and, importantly, how quickly a hostile incident could develop.

There was little value in writing an impressive emergency procedure if it was physically impossible to deliver when we actually needed it.

So we called our procedure:

Fallback.

That wording was deliberate.

We weren't pretending we could gather every customer, account for everybody and neatly move the entire venue into one protected room.

The strategy was about identifying places people could fall back to if the threat was outside or approaching the venue.

The objective was straightforward:

Move as many people as reasonably possible away from the threat and towards areas offering greater protection, while securing the premises where appropriate.

It wasn't perfect.

No emergency plan ever will be.

But it was achievable.

And I'd take an achievable emergency plan over an impressive-looking document that falls apart in the first 30 seconds of a real incident every time.

Does invacuation mean putting everyone into one room?

No.

And I think this is an important misconception.

Invacuation is about moving people away from danger to somewhere within the premises or event where there is less risk of physical harm.

That could mean bringing people who are outside into the building.

It could mean moving people from the front of a building towards the rear.

It could mean moving people into predetermined safer areas.

And depending on the premises, there may be more than one suitable area.

Current UK guidance specifically says organisations should consider safer areas with sufficient capacity and notes that these might include locations away from windows, external walls and entry points.

The word capacity is important.

If your designated safer area can hold 100 people and your venue has 800 people in it, writing:

“Invacuate customers to the safe area”

isn't a realistic plan.

What happens to the other 700?

That's exactly the sort of question I think needs to be asked while writing the plan, rather than during the incident.

What is a fallback strategy?

“Fallback” isn't a replacement for the recognised terms evacuation, invacuation or lockdown.

It's terminology I've used operationally to describe a practical response where moving everybody to one predetermined internal location isn't realistic.

The principle is simple:

If people cannot safely evacuate and you cannot realistically invacuate everyone to one location, where can different groups fall back to in order to increase their protection from the threat?

That requires an understanding of the actual building.

Where are the more substantial areas?

Where are people away from glazing?

Where are the alternative exits?

Which doors can be secured?

What areas have sufficient capacity?

Where could customers already in different parts of the premises move quickly?

What happens to people outside?

And can those movements be achieved without moving people towards the threat?

For me, that's protective-security planning.

It's not about finding the perfect terminology.

It's about working out what could actually be done.

Can evacuation, invacuation and lockdown be used together?

Yes.

And this is another reason I dislike overly rigid emergency procedures.

A real terrorist or hostile incident may not fit neatly into one box.

You might initially bring people inside.

Then secure the external doors.

Move customers away from the front of the building.

Keep one group where they are because moving them would expose them to greater danger.

Prevent additional people entering.

Then, once more information becomes available, evacuate another group through a different exit away from the threat.

The response can change as the incident changes.

Current statutory guidance explicitly recognises that multiple procedures may need to operate together or sequentially, and that plans may need to change in real time as the situation develops.

That isn't the emergency plan failing.

That's the emergency plan allowing people to respond to reality.

Why the nearest emergency exit may not be the safest exit

This is another important distinction between conventional evacuation thinking and a hostile incident.

The nearest available exit isn't automatically the safest exit.

Imagine an attack is taking place on one side of a building.

Sending people through the nearest exit on that side simply because it is their normal evacuation route could expose them to the threat.

A more appropriate response may involve directing people towards selected exits on the opposite side of the premises.

That means staff need to understand more than the location of their nearest fire exit.

They need to understand alternative routes.

People making decisions need situational awareness.

And information needs to reach staff controlling those routes quickly.

An emergency exit is a route out of a building. It isn't automatically a route to safety.

Should people go to the normal assembly point during a terrorist attack?

Not necessarily.

This is another area where automatically applying a fire procedure could create problems.

A predetermined assembly point is useful during a conventional fire evacuation because it helps move people away from the building and can support accountability.

During a hostile attack, creating a predictable concentration of people immediately outside the venue may be undesirable.

Current statutory guidance says organisations should consider whether people would be safer dispersing away from the premises and immediate vicinity rather than gathering at a predetermined nearby location. It specifically recognises that a predictable gathering point could potentially be exploited during an attack.

Again:

Where is the threat?

That's the question.

Not:

“Where does the emergency plan normally tell us to stand?”

What does an effective lockdown plan look like?

Lockdown is another term that sounds simple until you try to implement it.

“Lock the doors.”

Okay.

Which doors?

Who locks them?

How quickly?

Can they be secured from a safe position?

What happens to people approaching from outside?

Can some areas of the premises be secured independently?

Could locking one door accidentally prevent people escaping from another threat?

Can the lockdown be quickly reversed if the situation changes?

Who has the authority to initiate it?

How does everybody else know that lockdown has been activated?

Current guidance recognises several possible forms of lockdown, including full, partial, one-way, two-way and zonal approaches. It also emphasises the need to consider how existing doors, shutters and other barriers could actually be used.

So an instruction saying:

“In the event of a terrorist attack, lock the building down”

isn't really a lockdown plan.

It's an instruction without the operational detail required to make it happen.

Communication can determine whether the whole plan works

I think communication is sometimes treated as the final section of an emergency plan.

It should probably be one of the first.

Think about the difference between these instructions:

Get out.

Stay where you are.

Come inside.

Move away from the windows.

Don't use the front entrance.

Move towards the rear of the building.

Use Exit C only.

Those instructions could result in completely different movements of hundreds of people.

They need to be clear.

They need to reach people quickly.

And staff need to understand what they mean.

Depending on the premises, communication might involve radios, public-address systems, internal messaging, alarms or simply trained staff giving clear verbal instructions.

Current statutory guidance treats communication as one of the four public-protection procedures in its own right and says communication should provide information about danger and instructions on what people should do.

You can design an excellent evacuation, invacuation or lockdown procedure.

If nobody can communicate it when the incident starts, it isn't much use.

Who decides whether to evacuate, invacuate or lock down?

This needs to be considered before the incident.

Who has the authority to make the decision?

What information will they use?

How will they know where the threat is?

Who is monitoring CCTV?

Who is receiving reports from security officers or other staff?

Who contacts the emergency services?

Who communicates the decision to everybody else?

Current statutory guidance says public-protection planning should consider key roles and responsibilities, including who decides what action to take and who has authority to initiate procedures. It also recognises that reports from security staff and CCTV may contribute to a rapid assessment of what is happening.

That matters because a fast-moving hostile incident may not give you the luxury of holding a management meeting.

Someone may need to make a decision quickly.

Your plan needs to work in your building

This takes me back to the fallback strategy I developed after Borough Market.

One of the easiest things in security is writing an impressive procedure.

The harder part is standing in the actual building and asking:

Could we really do this?

Walk the site.

Look at the doors.

Look at the windows.

Look at the entrances.

Look at alternative exits.

Understand capacities.

Think about where customers naturally congregate.

Identify where people could realistically move.

Consider where a threat could originate.

Think about who would make the decision.

Work out how that decision would reach frontline staff.

Then test it.

Because if your plan relies on moving 1,000 people into an area that holds 200, you don't have a workable invacuation plan.

If your lockdown requires one person to run around manually securing 14 doors while an attack is taking place outside, I'd question whether you have a realistic lockdown plan.

And if every emergency automatically sends everybody to the same assembly point regardless of where the threat is located, I'd be reviewing that too.

The building should shape the emergency plan.

The emergency plan shouldn't pretend the building is something it isn't.

What should staff know about evacuation, invacuation and lockdown?

Staff don't necessarily need to become counter-terrorism specialists.

But they do need to understand the procedures they may be expected to carry out.

They should understand that a hostile incident may require a different response from a fire.

They should know the available exits and alternative routes.

They should understand where predetermined safer areas are.

They should know how a lockdown is initiated.

They should understand how instructions will be communicated.

And, importantly, they should understand that circumstances can change.

The current statutory guidance similarly requires those responsible for qualifying premises and events to consider appropriate and reasonably practicable procedures and to ensure relevant staff are adequately informed and, where appropriate, trained or instructed in implementing them.

A procedure sitting in a folder isn't the same as a procedure people can actually carry out.

The questions I'd ask every venue

Most organisations can answer this immediately:

“What do you do if the fire alarm activates?”

I'd ask three more questions.

What do you do if somebody is attacking people immediately outside your main entrance?

What do you do if the attacker is already inside the building?

What do you do if you don't yet know where the threat is?

If the answer to all three is:

“Evacuate.”

I'd be reviewing the plan.

I'm not advocating complicated emergency procedures.

Actually, the opposite.

When something serious happens, frontline staff need simple options that they understand and have practised.

But the people developing those procedures need to recognise that different threats can require very different responses.

Evacuate.

Invacuate.

Lock down.

Fall back.

Move people directionally.

Keep people where they are.

Or use several of those options as the situation develops.

For me, the terminology is secondary to one fundamental question:

Where are people safest right now?

Because during a terrorist or other hostile incident, the objective isn't to follow the emergency plan perfectly.

The objective is to move people away from danger and reduce the risk of harm.

Frequently Asked Questions

What is invacuation?

Invacuation means moving people away from danger to a safer location within a premises or event. It can include bringing people inside from outside or moving people from one part of a building to another where there is less risk of physical harm.

What is the difference between invacuation and lockdown?

Invacuation is about moving people to a safer location within the premises or event. Lockdown is about securing all or part of the premises to prevent or restrict people entering or leaving. The two procedures can be used together depending on the circumstances.

Should you evacuate during a terrorist attack?

It depends on the location and nature of the threat. If the threat is inside the premises, evacuation may be appropriate. If the threat is outside, invacuation or lockdown may provide greater protection. The response may also need to change as the incident develops.

Is a fire evacuation plan suitable for a terrorist attack?

Not necessarily. Fire and terrorist incidents can require different responses. Current UK guidance specifically says organisations should consider how terrorist-attack evacuation procedures complement rather than conflict with fire procedures, including the possibility that a normal fire alarm could prompt an inappropriate response to a hostile threat.

What is a fallback strategy?

Fallback is terminology I have used operationally for a strategy designed to move people away from a threat towards safer areas when complete invacuation to a single predetermined location isn't realistic. It doesn't replace the recognised terms evacuation, invacuation or lockdown; it describes a practical way of planning how different groups might move towards greater protection within the constraints of a real building.

What are the four public-protection procedures under Martyn's Law?

The four procedures identified under the Terrorism (Protection of Premises) Act 2025 are evacuation, invacuation, lockdown and communication. Organisations within scope must consider what procedures are appropriate and reasonably practicable for their particular premises or event.

Need to know whether your emergency plan would actually work?

It's easy to write “evacuate”, “invacuate” or “lockdown” into an emergency plan.

The important question is whether those procedures would actually work with your building, your staff and the number of people you are responsible for.

Blue Light Security Solutions can support organisations with security risk assessments, protective-security reviews and emergency planning, including evacuation, invacuation, lockdown and communication arrangements.

Our focus is practical:

What is the threat? Where are your people safer? And can the plan actually be delivered when you need it?

Contact Blue Light Security Solutions to discuss your emergency and protective-security arrangements.

0800 999 1829
office@bluelightgroup.uk