When the United States Postal Service (USPS) cancels mail delivery, you know the weather is extreme. Large sections of the East and Midwest are shivering under bitterly cold temperatures that have affected mail delivery, caused the cancellation of nearly 1,000 flights at O’Hare International Airport in Chicago and even halted Amtrak train service to and from the Windy City.

The arctic air mass, caused by a polar vortex system coming down from the north, is being blamed for at least seven deaths, according to news sources. Two of the victims were elderly residents of Illinois and Indiana who were found outside of their homes. Another was found frozen in his Milwaukee County, Wisconsin garage after apparently shoveling snow. An Indiana man appeared to have fallen in his driveway and died from exposure. Others were victims of weather-related motor vehicle accidents.

Employers should allow outdoor workers to suspend work during extreme cold or to take frequent breaks indoors. Click here for more information on how to protect outdoor workers from frigid temperatures.

Officials are reminding people to check on at-risk neighbors and to bring their pets indoors.

An estimated 230 million Americans are being affected by the cold. The frigid temperatures are expected to continue today before easing - somewhat - tomorrow, with many affected areas seeing temperatures rising up into the teens.

Frostbite and hypothermia can occur within a matter of minutes in extremely cold temperatures.

Frostbite symptoms include:

• Cold skin and a prickling feeling
• Numbness
• Red, white, bluish-white or grayish-yellow skin
• Hard or waxy-looking skin
• Clumsiness due to joint and muscle stiffness
• Blistering after rewarming, in severe cases

Hypothermia symptoms include:

• Shivering
• Slurred speech or mumbling
• Slow, shallow breathing
• Weak pulse
• Clumsiness or lack of coordination
• Drowsiness or very low energy
• Confusion or memory loss
• Loss of consciousness

People who think they’re suffering from frostbite or hypothermia should seek immediate medical treatment.

Contrary to popular opinion, “Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds,” is not the official motto of the USPS.