Guidelines for ALARA – As Low As Reasonably Achievable

Key points

  • ALARA is the guidance for radiation safety.
  • The three basic protective measures are time, distance, and shielding.
  • If there is a radiation emergency, use time, distance, and shielding to protect yourself and your family.
Female dental radiologist preparing male patient for dental computer tomography


The guiding principle of radiation safety is "ALARA." ALARA stands for "as low as reasonably achievable."

ALARA means avoiding exposure to radiation that does not have a direct benefit to you, even if the dose is small. To do this, you can use three basic protective measures in radiation safety: time, distance, and shielding.

Your action plan


"Time" refers to the amount of time you spend near a radioactive source. Minimize your time near a radioactive source to only what it takes to get the job done. If you are in an area where radiation levels are elevated:

  1. Complete your work as quickly as possible.
  2. Leave the area.

There is no reason to spend more time around the radioactive source than necessary.

Example: Imagine spending the day at the beach. If you stay in the sun the entire day, you will likely get sunburned. If are you are there for just a short period of time, you are less likely to get sunburned. The amount of time you are there makes a difference.


“Distance” refers to how close you are to a radioactive source. Maximize your distance from a radioactive source as much as you can. If you increase your distance, you decrease your dose.

Example: Imagine sitting very close to a fireplace. You can feel the heat and may even be uncomfortable. If you go to the other side of the room, you would be more comfortable. So as you move away, the intensity decreases.


To shield yourself from a radiation source, you need to put something between you and the radiation source. The most effective shielding will depend on what kind of radiation the source is emitting. Some radionuclides emit more than one kind of radiation.

Depending on the type of radiation something as thing as a sheet of paper may shield you. Other types may require a few inches of lead or another dense substance.

Time, distance, and shielding: Three principles that work together

You can see how these principles work together when you have an x-ray at your doctor’s office or clinic. The radiation technician goes behind a barrier while taking the x-ray image. The barrier protects them from repeated daily exposure to radiation.

Female Dental Radiologist Preparing Male Patient for Dental Computer Tomography
Example of using a lead vest for radiation shielding.

What to do in an emergency

If there is a radiation emergency, use time, distance, and shielding to protect yourself and your family.


If a radiation emergency happens, get inside a stable building as quickly as possible.


Where (how far away from the radiation source) you need to stay inside will depend on

  • The type and magnitude of the incident.
  • The amount of damage to critical infrastructure, like roads and bridges.

Emergency officials will instruct you when it is safe to leave the area.


  • If you are in a multistory building, move to the center floors.
  • If you are in a single story building, stay in the center away from windows, doors, and exterior walls.
  • You can also take shelter in a basement.

Using personal protective equipment

If you are a first responder or radiation worker, you can use personal protective equipment (PPE) to minimize your exposure.

  • Respirators will help protect from inhalation hazards.
  • Protective clothing helps keep radioactive material off skin and hair.
  • Alarming dosimeters (a personal radiation detector) help manage stay time and track your accumulated doses in an area with elevated radiation levels.

Anybody who works with radiation should work with their safety officers and radiation safety professionals. They should work together to determine PPE and instrumentation needed to stay safe.

If radioactive material gets on skin, clothing, or hair, it's important to get it off as quickly as possible. Learn how to self-decontaminate after a radiation emergency.