Transport Index Accumulation on a Multi-Drop Run
A carrier plans a single-vehicle multi-drop road run with five stops. The manifest lists: two Category II-YELLOW packages at TI 3.0 each; four II-YELLOW packages at TI 1.5 each; one III-YELLOW package at TI 8.0; and one III-YELLOW overpack whose label shows TI 4.0 with a handwritten note 'contains 2 packages, contents TI 6.2'. The dispatcher has totalled only the printed labels and concluded the load is acceptable. The van is unmarked, has no partition, and the driver would be alone for a 9-hour shift. The company has never used exclusive-use provisions and the operations manager is reluctant to start, because 'it means more paperwork and we'd have to placard the vehicle'.
1. Calculate the transport index that applies to this consignment and state whether the planned run is permissible as loaded.
Read the worked answer
Sum the package TIs, using the correct value for the overpack.
- 2 × TI 3.0 = 6.0
- 4 × TI 1.5 = 6.0
- 1 × TI 8.0 = 8.0
- Overpack: the TI of an overpack is the sum of the transport indexes of the packages inside, not a value chosen by the consignor. The note gives contents TI 6.2, so 6.2 applies, not 4.0.
Total = 6.0 + 6.0 + 8.0 + 6.2 = 26.2.
The threshold for a non-exclusive-use conveyance is a summed TI of 10. At 26.2 the load is roughly two and a half times over, so the run is not permissible as planned, whatever the dispatcher's addition shows.
The available routes out are: split the consignment across vehicles so each stays at or below 10; or operate the load under exclusive use, where the summed-TI limit falls away but must be replaced by the exclusive-use conditions - radiation level at the conveyance surface not above 2 mSv/h, not above 0.1 mSv/h at 2 m from the surface, the vehicle marked accordingly, and access and loading controlled. The manager's objection that exclusive use means 'more paperwork' is exactly backwards: it is the legal mechanism that makes this load possible, and it carries real operating duties rather than being a label.
2. What do you do about the overpack discrepancy, and why is it more serious than an arithmetic slip?
Read the worked answer
Do not accept the overpack for transport until the consignor re-issues the documentation.
The defect is not clerical. The transport index is the number on which segregation, dose estimates, conveyance limits and emergency response are all built. If the label says 4.0 and the contents justify 6.2, then every downstream calculation - including the total computed in the previous question - is wrong. A consignor who under-declares by a third on one overpack has given you no reason to trust the other labels on the same manifest.
The practical sequence:
- Segregate the overpack in a controlled position and record why it was held.
- Verify the radiation level yourself at 1 m; the TI should be consistent with it, allowing for measuring geometry and instrument response.
- Contact the consignor for a corrected overpack label and a corrected consignment note, and record the exchange.
- Re-total the consignment after correction and re-run the compliance check, because the true total may be higher than 26.2.
None of this is negotiable in exchange for keeping the delivery schedule. Accepting a known-bad label converts a consignor's error into the carrier's offence.
3. The route passes a school at 08:15. How much weight should that carry in the decision, and what actually controls the risk?
Read the worked answer
Less weight than it feels like, and it should not become the deciding argument.
The risk from a passing vehicle is set by the package radiation levels and the time people spend near them. With a summed TI of 26.2, the unshielded dose rate at 1 m is of the order of 0.26 mSv/h in the immediate vicinity of the packages - but that falls with the square of distance, and a vehicle passing a school gate at normal road speed delivers an utterly negligible dose to anyone inside the building. Treating a school on the route as a hazard in itself produces decisions based on alarm rather than numbers.
What actually controls the risk:
- The summed-TI limit and the chosen compliance route (split load or exclusive use), which determine whether the load may move at all.
- Load security and segregation, so packages cannot shift and cannot be approached casually at stops.
- Driver dose and occupancy, which is where the real cumulative exposure sits, not at the roadside.
- Any national routeing or escort requirements that apply to the class of consignment; if such requirements exist they are mandatory, and if they do not, improvised detours are not a substitute for the limits above.
The correct framing for the dispatcher: fix the TI problem and the driver dose, and the school question answers itself.