Heathrow Airport shut down by electrical substation fire: FAQs

Heathrow Airport in London will be closed all day today as a major power outage disrupts thousands of flights.

A fire broke out at a nearby electrical substation in the early hours of the morning, damaging equipment and leading to the power cut. About 70 firefighters worked to put out a transformer that had gone up in flames.

It's believed this is the first time in 15 years that Heathrow Airport has been completely shut. The outage also affected 4,900 homes in the area.

The following provides answers to frequently asked questions about the incident.

What is an electrical substation?

A substation is a ‘stopping point’ for electricity on its journey from where it’s generated to where it will be used. They help manage this flow safely and efficiently.

To travel long distances, electricity has to be very strong, so its power doesn't get lost. Think of it like a really powerful horse charging around at a gallop. You can't ride that!

So, it needs to 'calm down’ before it can be used safely in our buildings - this is essentially what substations are for.

Why can incidents such as a fire cause significant outages?

Simply because of the amount of power we're dealing with.

Using the horse analogy again, if a galloping horse hits something, it's going to break probably itself and whatever it hits.

Meanwhile, a horse travelling at a more controlled pace is much less likely to do damage.

Do fires often break out at substations?

Fires at substations are very rare, because they are usually very well managed because electricity is so dangerous. That's why the public aren't allowed anywhere near them.

If a substation breaks down, then the strong and powerful electricity could cause a lot of damage.

Usually, high-voltage (really powerful) electricity can go up in flames when it short-circuits, or meets an obstacle, which could be what happened here.

This will cause further damage to the substation and prevent it from delivering electricity to users.

What are the causes of fires at substations?

Anything that stops the flow of electricity unexpectedly can cause an electrical fire.

It could be as simple as a tree branch, or a bird or animal got into the substation and caused a short-circuit which started the fire.

It could have been equipment failure.

It's really difficult to speculate as it's such sensitive equipment.

All we know is substations are very well managed, especially for critical infrastructure like Heathrow, so this is not likely to have been predictable.

Is it normal for a substation fire to affect the running of an airport?

There are usually safeguards and spare power supplies for critical infrastructure like airports.

This can be in the form of back-up generators onsite, or a separate power supply that comes from a different place.

This creates resilience, so that if one supply breaks down, the lights stay on.

For some reason, this substation fire has knocked out all the power to Heathrow, which is a really unusual event, and only the grid operators will know exactly what's happened.

This incident is ‘unprecedented’ because there is no back-up power is keeping the airport operational. That is very surprising.

What substation equipment can be damaged by a fire?

The fire damaged a transformer, devices that reduce or ‘calm’ the power voltage from very high to usable levels.

The cables that were short-circuited will likely be damaged as well.

How will the power be restored, and how long will it take?

There will be a lot of people working very hard to redirect electricity in different ways to try and get the power on, and other people fixing the damaged substation.

There's likely to be a lot of people working overtime for several weeks or even months to deal with the consequences of this.

How will the substation operator find out what caused the fire?

There will be people onsite at the substation trying to figure out what caused the fire, likely emergency services and grid network operators.

There will be a combination of looking at things on the ground as well as looking at what was happening on the electrical grid in the hours and minutes leading up to the fire.