Free interactive tool
Set a dose budget and a measured field rate, and work out how long you can stay before reaching it — or, for a planned stay, the dose you'd take. Choose a steady source or a decaying fresh-fallout field. This is the operational counterpart to the dose calculator's acute-exposure table. Everything runs here on the page — no sign-up, nothing stored.
Your budget is your dose limit minus any dose you've already taken. In a steady field, stay time is simply budget ÷ rate. In fresh fallout the rate falls following the 7-10 rule, so you can often stay longer — and a high budget may never be reached, because the field decays away first.
Your dose budget
How long you can stay
Using up your budget
| Budget used | Dose | Time to reach |
|---|---|---|
| 25% | 62.5 mSv | 12.5 hr |
| 50% | 125 mSv | 25 hr |
| 75% | 187.5 mSv | 37.5 hr |
| 100% | 250 mSv | 50 hr |
The dose limits here are approximate operational reference levels from occupational and emergency-worker guidance (ICRP / IAEA / EPA). The exact figures vary by country and situation and are not hard rules — real decisions are made by qualified responders with proper instruments.
For safety, treat a field as steady unless you genuinely know the time since the blast and that fallout is the only source — the steady stay time is always the shorter, more conservative answer. Shielding and distance cut the rate (and so extend your time), and a budget is a planning aid, not a guarantee of safety.
To convert a dose rate between units, or see acute-exposure (ARS) timeframes, use the dose & exposure converter.
Fresh fallout is a mix of hundreds of fission products whose combined dose rate falls along the empirical 7-10 rule: R(t) = R₁ · t−1.2, where t is hours after the detonation and R₁ is the rate at one hour. Enter the rate your instrument reads now and how many hours it's been since the blast; the tool back-calculates R₁ and integrates the dose over your stay.
Because the rate keeps falling, the dose you accumulate converges: starting at t hours, the most you could ever take — even staying forever — is about 5 × (current rate) × t. That's why a large budget can read as "no limit" here. It's the same convergence behind the dose calculator's fallout figures; this tool just turns it into an operational stay time. For a single known isotope (clean exponential decay, not the 7-10 mixture), use the isotope half-life decay calculator.