Ambulances are being stocked with extra blankets and towels, and the heater is being cranked way up.

School bus mechanics will get to work early to make sure that buses will start, and that students are warm on their ride to school.

And furnace companies, who typically get a break this time of year, are booked.

Brace yourself for bitter cold temperatures starting today. Low temperatures will dip below zero today and Thursday, according to the National Weather Service. Temperatures won’t peak above freezing again until the weekend.

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In the hours before the frigid cold arrived, fire departments, schools and businesses were preparing.

The snow and ice lingering from earlier this week increases the chances that people will get hurt in car crashes or slip and fall while walking outdoors. Along with those calls, local ambulances still have to respond to severe illnesses and emergencies. With the outside air so bitter, protecting patients from the elements is an extra step in providing care, local fire departments said.

“We’re very vigilant that these patients are exposed, and not only are you trying to treat whatever is wrong with them, but watching out for hypothermia, which can set in really fast,” Franklin Fire Department spokesman Brad Epperson said.

So when emergency medical workers are getting a patient out of a wrecked car or their home, they wrap them in blankets like a burrito, and they’re quickly whisked into back of the ambulance.

“Sometimes we cover them up and cover up their whole face with a towel if they’re OK with that. We’re going to cover you up and make sure you get warm. It’s not uncommon to wrap them up like a burrito,” Greenwood Division Chief of Emergency Medical Services Darin Hoggatt said.

Speed is the first key, to minimize the amount of time someone will be outside. Firefighters don’t want frostbite or hypothermia added to the problems a patient is having.

Keeping a patient warm can be more difficult in events, such as a slip-and-fall at the mailbox, when a person has already been lying in the snow or the cold ground, Epperson said. Firefighters will get a warm blanket over them as quickly as possible, but medics have to check for any neck, head or spine injuries before being able to lift someone up and get them into the ambulance, he said.

In good weather, a person may sit on the side of the road or on the bumper of the ambulance to get scrapes or cuts cleaned up after a car crash. But in extreme cold, firefighters are focusing on getting that person inside the back of the ambulance and closing the door as soon as possible, Hoggatt said.

When out on a call, the heat is always turned up in the back to make sure the patient will be warm if they’re not wearing a coat or other cold weather gear, Epperson said. It’s kept so warm that a paramedic or firefighter, who is dressed for the weather, is going to be feeling hot.

“They keep the back of the ambulance really toasty. Sometimes it’s uncomfortable for them and the fire person if they’re riding along, but the goal is to make sure that patient is warm,” Epperson said.

The low temperatures also mean that school bus mechanics have to arrive at work earlier than usual to warm up the vehicles, and to ensure they’ll start.

Greenwood schools starts their buses about 4:30 a.m. — about 90 minutes earlier than normal — anytime the temperature dips below 10 degrees. That’s partly to ensure that the buses are warm as they pick up students, but also because the further the temperature falls, the more difficult it is to start the engine, Greenwood director of operations Mike Hildebrand said.

“They’re good and warm as they’re leaving our lot to go for that first stop,” Hildebrand said.

When the temperature falls to 10 below zero, that’s when school superintendents start considering calling for a two-hour delay or to cancel classes altogether.

Two hours doesn’t always mean the temperatures will be warm enough for students to be standing outside at the bus stops, since frostbite can start within minutes, Hildebrand said.

But a two-hour delay does allow drivers to pick students up in daylight, meaning they can watch for students coming from inside houses and cars around the bus stop, Hildebrand said.

He said he hopes wherever students are waiting is warm. And this week, that is a top focus of heating and air conditioning companies.

This time of the year, most residents already had their furnace checked by local heating and cooling professionals. But with the temperatures dipping below zero and then spiking back up to 50 degrees, that can take a toll on the furnace, said Bill Miller, owner of Bill Miller Heating and Cooling. The furnace becomes overworked and can eventually break as the machine is trying to adjust to the temperature, he said.

But before you call for a repair, they suggest you check one thing: your furnace filter, which should be replaced every 30 days, DuganAir owner Dan Dugan said.

If the air filter gets too dirty, it can cause the furnace to overheat, Miller said. About 50 percent of Miller’s customers have had an issue with their air filter, causing their system to work improperly, he said.