According to firefighters, every second counts during a fire. In fact, house fires can double in size every minute that goes by. About half of home fire deaths happen between 11 p.m. and 7 a.m. when most people are sleeping.

But here’s the good news: There’s a simple step you can add to your nighttime routine to keep you safe.

Research from Underwriters Laboratories Firefighter Safety Research Institute (FRSI) shows that closing your bedroom door helps prevent a fire from spreading, lessens smoke damage and could even save lives.

Just like having the right homeowners insurance, a little preparation can go a long way to help you rest easy.

Here’s why it works: The more oxygen a fire has, the quicker it will spread. Keeping your bedroom door closed has been proven to slow the spread of a house fire. Additional benefits include reduction of toxic smoke levels and lower levels of heat inside the bedroom. It is important to note – within 60 seconds of a fire starting, ceiling temperatures can reach over 1,000° F.

Having the right kind of fire extinguisher nearby can also help. But when it comes to fire-related deaths, it’s usually not the flames that are to blame. Smoke and heat are actually more likely to cause suffocation and death.

Why Should You Sleep With the Door Closed?

When a door is closed during a fire, a person in that room experiences:

  • More survivable temperatures: Temperatures typically stay below 100 degrees Fahrenheit.
  • Livable oxygen levels: Oxygen levels read around 18%. (For comparison, regular room air is about 21% oxygen.)
  • Less toxic carbon monoxide levels: Close to 100 parts per million (PPM) of carbon monoxide (CO).

When a door remains open during a fire, a person in that room is exposed to:

  • Less survivable temperatures: Temperatures can get hotter than 1,000 degrees Fahrenheit.
  • Low oxygen levels: Oxygen levels can decrease to 8%, making it harder to breathe.
  • Extremely toxic carbon monoxide levels: Dangerous levels can increase to 10,000 PPM of CO.

How Much Time Do You Have to Escape a Fire?

Forty years ago, the average time people had to safely escape a fire was 17 minutes. Today’s homes only allow for three minutes or less to evacuate. Why? Modern synthetic construction materials, lower quality components, home furnishings and contemporary layouts allow fire to spread and become toxic much faster than in the past.

But don’t panic — even three minutes is a lot of time to escape a fire if you remain calm, have a plan and close doors in your home. One way to prepare is by establishing a fire escape plan with your family and practicing it twice a year. (It’s also a good idea to test your smoke alarms once a month to ensure they work properly and that everyone knows what they sound like.)

While you’re practicing your fire escape plans, remember to cover these additional safety tips:

  • Roll off your bed, don’t stand up if your smoke alarm wakes you up from sleep.
  • Use the back of your hand to test your door for heat (and don’t grab the doorknob – it could be HOT). If it’s cold you can open the door, but if it’s hot, you need to find another exit.
  • Crawl, don’t walk, if there’s heavy smoke in your home. Heat and smoke rise, so cooler, fresher air is low to the ground.
  • Never go back in for pets or other people. Your safety is the most important.
  • Remember Stop, Drop and Roll if your clothes catch on fire.

One final tip: When you escape a fire, remember to close the door behind you once you exit. This will cut off the oxygen to the fire and may stop the fire’s growth.