"The reason is that there is a very concrete European Union directive for natural gas and heating that says home consumers are a priority and must be switched off last. It also makes sense as heating is crucial for people's survival and normal functioning," said Priit Saar, head of the crisis regulation department of the Ministry of Economic Affairs and Communications (MKM).

Vital service rules for electricity prioritize objects on which people's lives and health directly depend, with hospitals, nursing homes and alarm centers topping the list. The 112 emergency hotline must remain available as it coordinates the activities of the police, firefighters and emergency response, Saar explained.

"But to ensure people have heating – for boiler plants and pumping stations to work to move water around and keep district heating going – we have placed in the second category the critical infrastructure of other vital service providers, including district heating and waterworks," the MKM department chief added. "They also include communications providers, critical telecommunications infrastructure, as well as filling stations to ensure access to liquid fuel reserves," he went on. "It is like an additional layer of protection, while all of these critical enterprises must also have autonomous power systems," Saar noted.

"And in the third, fourth and fifth categories come other consumers. Indeed, people's homes, apartment buildings fall in the fifth column," he added.

Various industrial companies and public places – such as shopping malls, theaters, gyms – take higher priority than residences. Saar emphasized that the list of priorities is regularly updated and complemented.

He said that grid operator Elektrilevi stays in touch with customers and tells them which priority group they belong to.

However, the list is not a public document as it would give too much critical information to Estonia's enemies, Saar noted. "Such a general description constitutes public information, while a specific list of companies affected cannot be circulated as the information is too sensitive. Especially in the Elektrilevi information system that also reflects objects' infrastructure parameters that would clearly be too sensitive. But in general, we have five categories and who they cover is public information."

Switch-off rotation

Saar explained that switching off power to residential buildings would usually happen in rotations of a few hours – so that no residential area would be without power too long.

"If we are only short a few dozen megawatts, transmission network operator Elering notifies Elektrilevi of a deficit in a certain area. The latter will then look at its infrastructure map and switch off consumers that least affect public services. This would happen as a rotation of power cuts of a few hours. So that no area would be left without power for long," he said.

Saar added that any such decisions would also depend on the situation, season and how much output is missing.

The department head said that no such rotation of power cuts has taken place in Estonia, while there have been theoretical exercises and crisis plans exist. "It is the main scenario should we experience more serious power supply disruptions."

"If we know we will be short on power, we can draw up the rotation plans and notify customers," said Rasmus Armas, head of property management for Elektrilevi.

Cuts automatic in extraordinary situation

Were the network to experience a sudden and major power shortage, lower category consumers would be switched off automatically, Saar explained. "But that would be an extreme eventuality we do not hold likely at this time as we have enough power for that in different phases. And it would not concern the top categories.

"Because capacity and consumption need to be balanced, switch-offs would hit consumers who can be disconnected the fastest," Saar said, adding that this might not leave enough time to coordinate the decisions.

Rasmus Armas said that switch-offs would run along medium voltage power lines. "There is no street-level connection, while we are talking about areas larger than a block. Medium voltage lines that we can switch off number 256 and cover over 50 percent of total consumption in Estonia."

Priit Saar emphasized that higher category institutions, like hospitals, ISPs and many others, should have autonomous power for extreme crisis situations, like war, major cyberattacks or violent storms.

Outages of two hours optimal

Saar said that two-hour outages have been considered in crisis plans as that would not yet result in serious consequences during periods of cold weather.

"This would not yet see pipes freeze. But anything longer than that could make life uncomfortable for people and cause property damage," he said.

Water and heating require electricity

Because the water and heating systems of apartment buildings usually rely on their electrical system, power outages would also hit them, Armas said.

A spokesperson for Tallinn's district heater Utilitas said as much. "If apartment buildings lose power, circulation pumps and automatic systems also grind to a halt," Olga Petrova said.

While Utilitas would continue sending hot water to buildings, their own systems being out of commission would make it impossible to pump water into apartments' pipes or radiators. To avoid this, apartment buildings would need reserve power systems, Petrova added.

Priit Saar said that apartment association have been consulted on the need to install backup generators.

"But if the outages do not last more than two hours, people should be fine and there should be no need to fire up backup generators in apartment buildings," he said.

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