Radiation Surveys and Dose Rate Limits Before Shipping

Why the Pre-Shipment Survey Matters

The radiation survey is the one step in Class 7 shipping where the package itself testifies. The numbers on the label — the TI and the category — are declarations about physical measurements, and anyone with a meter can check them: a DOT inspector, a carrier acceptance agent, or the consignee's RSO. If the package reads hotter than the label says, you have a violation in transit with your name on the shipping paper.

The limits exist to protect people who never signed up for radiation exposure: drivers, dock workers, sorters, and the public. You are not checking a box — you are certifying that a stranger can handle this package safely.

I treat the survey as the last gate before release. In fifteen years I have never regretted the ten extra minutes it takes, and I have watched more than one shipment come back because somebody else's survey was rushed.

Who Needs to Know This

This applies to anyone who:

• Performs or reviews pre-shipment radiation surveys on Class 7 packages
• Assigns the TI and selects the label category for outgoing packages
• Runs wipe tests on packages, overpacks, or vehicles
• Supervises shippers and needs to know what “surveyed and within limits” actually requires

How to Survey a Package Before Shipping

The survey answers two questions: what is the maximum dose rate at the package surface, and what is the maximum dose rate at 1 meter? The first tells you whether the package can ship as a normal package; the second gives you the transport index.

Step 1: Check Your Instrument

Use a dose rate meter appropriate for the radiation type and energy you are shipping, with a current calibration — for most gamma-emitting shipments, an ion chamber or an energy-compensated GM detector. The regulations set the limits, not the instrument; your radiation safety program and your carrier's requirements govern meter selection and calibration frequency. Before every survey: check the calibration sticker, check the battery, and source-check the response if your program provides a check source.

My habit before every survey is thirty seconds of background reading away from the package. If the meter will not settle on a believable background, it will not give you a believable surface reading either — a dying battery or a cold instrument will happily display a number anyway.

Step 2: Survey All Accessible Surfaces

Move the probe slowly over every external surface of the package — top, all four sides, and the bottom — and record the highest reading you find. The 173.441(a) limit applies “at any point on the external surface,” not at the average point or the convenient point. Tip the package (safely) or use the gap on a pallet jack to get the underside.

The mistake I see most often is skipping the bottom. Shielding pigs sit on the floor of the box, and the thinnest shielding path is frequently straight down — I have measured packages that read comfortably on all four sides and peaked on the underside. If your survey record shows five readings and none of them is the bottom, an experienced inspector will notice.

Step 3: Survey at 1 Meter and Assign the TI

Next, find the maximum reading at 1 m (3.3 ft) from the external surface. Under 49 CFR 173.403, the transport index is that maximum level in mrem per hour (mSv/h × 100), rounded up to the next tenth — 1.11 mrem/hr is a TI of 1.2, not 1.1. Readings at or below 0.05 mrem/hr round to a TI of 0. Our transport index guide covers what the TI controls downstream.

Measure 1 meter from the surface, not from the center of the package — and hold the geometry honest. A meter stick beats eyeballing it every time; I have watched people pace off “about a meter” and shave a label category without meaning to.

What Are the Dose Rate Limits for a Normal Shipment?

49 CFR 173.441(a) sets the two limits every non-exclusive use package must meet, designed and prepared so they hold “under conditions normally incident to transportation”:

• Surface limit: the radiation level may not exceed 200 mrem/h (2 mSv/h)our (200 mrem/hour) at any point on the external surface of the package
• Transport index limit: the TI may not exceed 10

These same measurements set the label category. As covered in our labeling basics guide: WHITE-I requires a surface reading no more than 0.5 mrem/hr; YELLOW-II allows TI up to 1 and surface up to 50 mrem/hr; YELLOW-III allows TI up to 10 and surface up to 200 mrem/hr. Sloppy readings produce wrong labels.

There is also a conveyance-level limit: under 173.441(d)(1), the sum of TIs on a non-exclusive use conveyance may not exceed 50 (separate provisions apply to cargo aircraft and vessels). That is the carrier's number to manage, but it is why your TI matters to them — your package consumes part of their budget.

Exclusive Use: The Limits When a Package Runs Hot

A package that exceeds the 173.441(a) limits is not unshippable — it must move as an exclusive use shipment under 173.441(b), meaning a single consignor controls the conveyance and all loading and unloading. Exclusive use trades higher package limits for limits on the vehicle itself:

• Package surface — 200 mrem/h (2 mSv/h), unless three conditions are all met, in which case the limit rises to 1000 mrem/h (10 mSv/h): the shipment is in a closed transport vehicle, the package is secured so its position remains fixed during transportation, and there are no loading or unloading operations between the beginning and end of the transportation
• Vehicle outer surfaces — 200 mrem/h (2 mSv/h) at any point, including the top and underside of the vehicle (for a flat-bed, measured at the vertical planes projected from the outer edges, the upper surface of the load or enclosure, and the lower external surface)
• 2 m (6.6 feet) from the outer lateral surfaces of the vehicle — 10 mrem/h (0.1 mSv/h), excluding the top and underside
• Any normally occupied space — 2 mrem/h (0.02 mSv/h), unless the carrier operates under a State or federally regulated radiation protection program and the personnel in that space wear dosimetry

Under 173.441(c), the offeror — you, not the carrier — must provide specific written instructions for maintaining the exclusive use controls, included with the shipping paper information. Under 173.441(d)(2), there is no ceiling on the sum of TIs for an exclusive use conveyance, provided the vehicle-level limits are met.

If you ship exclusive use, the survey becomes a vehicle survey: you walk the loaded conveyance — sides, top if accessible, cab — and step out to 2 meters. The first time a carrier asked me for the cab reading in writing, I was glad I had already taken it. Carrier safety departments know these numbers, and a driver is entitled to ask what the reading is behind the seat.

Contamination Wipe Tests Under 173.443

Dose rate is only half the survey. 49 CFR 173.443 requires non-fixed (removable) contamination on package external surfaces to be kept as low as reasonably achievable, with hard limits in Table 9:

The standard method in 173.443(a)(1)(i): wipe an area of 300 cm² with an absorbent material using moderate pressure, take enough wipes in representative locations, and measure the activity on the wipe. The measured activity is divided by the area wiped and by the wipe efficiency — the fraction of removable contamination the wipe actually picked up. You may use your actual measured efficiency, or assume 0.10.

That efficiency division is the step people botch. Dividing by 0.10 multiplies your result by ten — a raw count that looks like a tenth of the limit is actually sitting at the limit. If your counting sheet does not show the efficiency factor explicitly, fix the sheet before an inspector fixes it for you.

One more provision worth knowing: for exclusive use shipments by rail or highway, 173.443(b) allows non-fixed contamination during transport up to ten times the Table 9 levels, but the levels at the beginning of transport may not exceed Table 9. Our contamination limits guide goes deeper on Table 9, wipe technique, and vehicle release surveys.

What If the Package Exceeds a Limit?

First: stop. Do not tender the package, and do not talk yourself into “probably meter error.” Then work the options in order:

1. Verify the measurement. Recheck calibration, background, and geometry; confirm with a second instrument if available.
2. Fix the package. Add or reposition shielding, re-center the source, or move to a larger package — distance is free shielding, and the same source in a bigger box reads lower at the surface.
3. Split the consignment. Two compliant packages beat one non-compliant package.
4. Decontaminate. If the wipe test failed, clean and re-wipe until you are under Table 9 — then ask why the outside of the package was contaminated in the first place.
5. Go exclusive use. If the package legitimately cannot meet 173.441(a), arrange an exclusive use shipment under 173.441(b), with the vehicle surveys and written carrier instructions that come with it.

One hard stop, straight from 173.441(e): a package exceeding the maximum surface radiation level or maximum transport index in paragraph (a) may not be transported by aircraft. There is no exclusive use workaround in the air — a hot package is a ground (or vessel) shipment, full stop.

The worst response I have seen to a high reading is re-surveying with a different meter until one gives the answer the shipper wanted. If two calibrated instruments disagree, the conservative reading ships — or the package does not.

Documenting Your Survey Results

A survey you cannot produce evidence for is, from an inspector's chair, a survey that may not have happened. A defensible survey record captures:

• Package identification tied to the shipping paper
• Instrument make, model, serial number, and calibration due date
• Background reading, maximum surface reading (with location — note if it was the bottom), and maximum 1 m reading
• The TI assigned and the label category selected, so the paper trail matches the package
• Wipe test results showing the raw counts, the area wiped, the efficiency applied, and the final value against Table 9
• Date, time, and the surveyor's name or signature

Keep the record with your shipping records. Carriers increasingly ask for survey documentation at acceptance for higher-TI packages, and consignees' RSOs often want it on receipt — their incoming survey gets compared to your outgoing one, and a mismatch triggers phone calls. I fill out the survey form at the package, meter in hand, not from memory at a desk twenty minutes later; transcribed-from-memory records have a way of being internally consistent and wrong.

How RadShip.com Helps

RadShip.com takes your survey readings and turns them into compliant shipping decisions:

• LabelCalc, our transport index calculator — enter your surface and 1 m readings and it computes the TI with the correct round-up, selects WHITE-I / YELLOW-II / YELLOW-III, and flags a package that busts the non-exclusive use limits before your carrier does
• RAMcalc — handles the classification side (UN number, package type, quantity limits) so the survey is confirming a well-designed shipment, not rescuing a bad one

The value is not that the math is hard — it is that the rounding rule, the category thresholds, and the exclusive use trigger all have to be applied correctly on every package, including the one you prepare at 4:45 on a Friday. A tool that applies them the same way every time removes the failure mode I have seen most: the experienced shipper who did it right four hundred times and slipped on number four hundred one.

Try it free for 7 days.

Common Questions

What is the dose rate limit on the surface of a radioactive package?

200 mrem/hour (2 mSv/hour) at any point on the external surface for a non-exclusive use shipment, per 49 CFR 173.441(a), with the transport index not exceeding 10. Packages over those limits must move as exclusive use shipments under 173.441(b).

How do I measure the transport index?

Maximum reading at 1 m (3.3 ft) from the package surface, in mrem/hr, rounded up to the next tenth. The 173.403 definition states it as the mSv/h reading multiplied by 100. Readings at or below 0.05 mrem/hr take a TI of 0. See the full TI guide for how the TI drives labels and conveyance limits.

What are the contamination wipe test limits?

4 Bq/cm² (240 dpm/cm²) for beta/gamma and low toxicity alpha emitters; 0.4 Bq/cm² (24 dpm/cm²) for all other alpha emitters — Table 9 of 49 CFR 173.443. Wipe 300 cm², then divide the measured activity by the area and by the wipe efficiency (assume 0.10 if unmeasured).

What happens if my package exceeds 200 mrem/hr on the surface?

It cannot ship as a normal package — exclusive use or nothing. Under 173.441(b) the surface limit can rise to 1000 mrem/h (10 mSv/h) only in a closed vehicle with the package secured and no intermediate loading or unloading. And per 173.441(e), a package over the 173.441(a) limits may not fly, period.

What instrument should I use for the pre-shipment survey?

A calibrated dose rate meter matched to your radiation type and energy — commonly an ion chamber or energy-compensated GM for gamma emitters, plus counting equipment for wipe samples. The CFR sets the limits, not the instrument list; your radiation safety program and carrier requirements govern selection and calibration.

Do I need to document the survey?

Yes — treat the survey record as part of the shipment file. The label's TI and category are declarations of measured values, and carriers, inspectors, and receiving RSOs all have reason to ask for the numbers behind them.

My overall take: the survey is the cheapest insurance in Class 7 shipping. Wrong labels, wrong categories, and receiver disputes all get caught or prevented by ten careful minutes with a calibrated meter and an honest form. Shippers who treat the survey as the point of the job, rather than the last chore before the truck, almost never see their packages come back.

Summary: Your Pre-Shipment Survey Checklist

Before tendering any Class 7 package, ensure:

• ☐ Meter has a current calibration sticker, good battery, and a believable background reading
• ☐ Package surveyed in final shipping configuration — closed, overpacked if applicable
• ☐ All external surfaces surveyed, including the bottom; maximum surface reading ≤ 200 mrem/hr (2 mSv/h) for non-exclusive use
• ☐ Maximum 1 m reading taken with honest geometry; TI rounded up to the next tenth, ≤ 10
• ☐ TI and surface readings support the label category on the package (WHITE-I / YELLOW-II / YELLOW-III)
• ☐ Wipe test taken over 300 cm², efficiency applied, result under Table 9 limits
• ☐ If exclusive use: vehicle surface, 2 m, and occupied-space readings taken and written carrier instructions prepared
• ☐ Survey record completed at the package — instrument, readings, locations, date, surveyor — and filed with the shipping paper

Regulatory References

DOT Requirements:

• 49 CFR 173.441 – Radiation level limitations and exclusive use provisions (surface limit, TI limit, exclusive use vehicle limits)
• 49 CFR 173.443 – Contamination control (Table 9 wipe test limits, exclusive use contamination provisions)
• 49 CFR 173.403 – Definitions (transport index, exclusive use)
• 49 CFR 172.403 – Class 7 label selection (category determined by TI and surface radiation level)

NRC Requirements:

• 10 CFR 71.47 – External radiation standards for all packages (parallel NRC requirements for licensees)

IATA (Air Transport):

• IATA Dangerous Goods Regulations, Section 10 – Radioactive material; air shipments must meet the non-exclusive use limits (49 CFR 173.441(e) bars packages exceeding the 173.441(a) limits from aircraft)