Gamma Rays — How Much is Too Much?

IMPORTANT: Radiation sickness is NOT contagious - it CAN NOT spread person-to-person.

This table gives a general guidelines of short-term, whole-body exposures (in roentgens) and likely effects for the average person. "Short-term" indicates exposure over a period of hours, days, or a couple of weeks. "Long-term" indicates periods of months or years. We are also referring to total accumulated exposure.

Roentgens Effect
15
 Smallest effect detectable by statistical study of blood counts of a group of people.
50
 Smallest effect detectable in an individual by laboratory methods.
75
 Smallest dose causing vomiting on day of exposure in at least 10% of people.
100
 Smallest dose causing loss of hair after 2 weeks in at least 10% of people.
200
 Largest dose that does not cause illness severe enough to require medical care in over 90% of people.
450
 Median lethal dose, fatal to 50% of people in 2 to 12 weeks.
600
 Severe sickness due to gastrointestinal tract damage, survivors unlikely.
2000-10000
 Death in minutes-to-1-day due to central nervous system damage.


These effects are lessened considerably if the dose is received over a long period of time. A short-term dose of 600 roentgens would probably be fatal, but if the exposure were gradually acquired over a much longer period (months to years) it would probably have no noticeable effects. For instance, if a person's total dose is 200 roentgens for the first month, 25 roentgens per week for the next 5 months, and 10 roentgens per week thereafter for the next 6 months, they would have little if any radiation sickness. The body will heal and repair some of the damage if the exposure is received gradually, allowing larger total doses.

Here is a similar chart detailing dosage effects expected in a group of people as condensed from a 1967 Defense Department shelter management textbook:

Roentgens
Effect
0-50
 No obvious effect.
80-120
 5-10% of exposed people will experience vomiting and nausea for 1 day.
Fatigue but no serious disability.
130-170
 25% will experience vomiting and nausea for 1 day, followed by other symptoms of radiation sickness.
No deaths anticipated.
180-220
 50% will experience vomiting and nausea for 1 day, followed by other symptoms of radiation sickness.
No deaths anticipated.
270-330
 Vomiting and nausea in nearly all people on first day, followed by symptoms of radiation sickness.
20% deaths within 2 to 6 weeks after exposure. Survivors convalescent for about 3 months.
400-500
 Vomiting and nausea in all people on first day, followed by symptoms of radiation sickness.
50% deaths within 1 month. Survivors convalescent for about 6 months.
550-750
 Vomiting and nausea in all people within 4 hours, followed by other symptoms of radiation sickness.
Up to 100% deaths. The few survivors will be convalescent for about 6 months.
1000
 Vomiting and nausea in all people within 1 to 2 hours.
Probably no survivors from radiation sickness.
5000
 Incapacitation almost immediately.
All people will be fatalities within 1 week.


When can I go outside?

Roentgens/hr Recommended Limits of Activity Outside the Fallout Shelter
Over 100
 Outdoor activity of more than a few minutes may result in sickness or death.
Go outside only to escape fire or to get to better shelter if it is only a few minutes away.
10 - 100
 Limit time outside to a few minutes and only for emergencies that can't be postponed a day.
2 - 10
 Less than an hour per day outside for the most essential purposes should be OK.
Shelter occupants should rotate outdoor tasks to minimize total doses.
0.5 - 2
 A few hours per day outside are tolerable. Eat and sleep in shelter.
under 0.5
 No special precautions. Sleep in shelter.