Class 7 (Radioactive Material) Basics, Activity Limits & Radiation Protection

Class 7 (Radioactive Material) Basics, Activity Limits & Radiation Protection

Class 7 (Radioactive Material) differs fundamentally from all other hazard classes because its hazard originates from nuclear physics—spontaneous atomic nuclear transformations resulting in ionizing radiation emission (alpha particles, beta particles, gamma rays, or neutrons)—rather than chemical reactions. The regulation of Class 7 under the IATA DGR incorporates standards established by the International Atomic Energy Agency (IAEA).

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Definition of Class 7 Radioactive Material

A material is classified as Class 7 if both of the following regulatory conditions are met:

1. The activity concentration of the radionuclide exceeds the activity concentration limit specified in IATA DGR Table 3.7.2; AND
2. The total activity of the consignment exceeds the total activity limit for an exempt consignment specified in Table 3.7.2.

Units of Radiation Measurement

• Activity ($A$): Measured in Becquerels (Bq), representing one disintegration per second. (Historically measured in Curies, $Ci$, where $1\text{ Ci} = 3.7 \times 10^{10}\text{ Bq}$).
• Equivalent Dose Rate: Measured in Sieverts per hour (Sv/h) or millisieverts per hour (mSv/h), representing biological dose equivalent. (Historically measured in rem/h, where $1\text{ mSv/h} = 100\text{ mrem/h}$ or $1\text{ }\mu\text{Sv/h} = 0.1\text{ mrem/h}$).

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Activity Limits: $A_1$ and $A_2$ Values

The IATA DGR specifies activity limits—known as $A_1$ and $A_2$ values (expressed in Gigabecquerels, $GBq$)—for every single radionuclide:

• $A_1$ Value: The maximum activity of special form radioactive material permitted in a Type A package.
  • Special form refers to an indispersible solid radioactive material or a sealed capsule containing radioactive material that can only be opened by destroying the capsule.
• $A_2$ Value: The maximum activity of normal form radioactive material permitted in a Type A package.
  • Normal form refers to radioactive material that does not qualify as special form (e.g., liquids, gases, unsealed powders).

Rule: If a consignment of radioactive material exceeds $A_1$ (for special form) or $A_2$ (for normal form), it cannot be shipped in a Type A package. It must be packaged in a Type B or Type C package.

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Class 7 Package Types

                                  CLASS 7 PACKAGE TYPES
  ┌──────────────────┬──────────────────┬──────────────────┬──────────────────┬──────────────────┐
  │ EXCEPTED PACKAGE │INDUSTRIAL PACKAGE│  TYPE A PACKAGE  │  TYPE B PACKAGE  │  TYPE C PACKAGE  │
  ├──────────────────┼──────────────────┼──────────────────┼──────────────────┼──────────────────┤
  │ Extremely low    │ Used for Low     │ Activity <= A1   │ Activity > A1/A2 │ Extremely high   │
  │ activity         │ Specific Activity│ (special form)   │ Severe accident  │ activity air     │
  │ (e.g. 10⁻³ A2).  │ (LSA) & SCO.     │ or <= A2 (normal)│ resistant test   │ transport        │
  │ Exempt labels.   │ IP-1, IP-2, IP-3.│ Normal air test. │ (drop, fire 800°C│ (high speed drop)│
  └──────────────────┴──────────────────┴──────────────────┴──────────────────┴──────────────────┘

1. Excepted Package: Contains activity levels so small (a fraction of $A_1$ or $A_2$, e.g., $\le 10^{-3} A_1$ or $10^{-4} A_2$) that package design requirements are minimal. Exempt from standard Class 7 hazard labels (requires Excepted Package mark).
2. Industrial Package (Type IP-1, IP-2, IP-3): Used for Low Specific Activity (LSA) materials and Surface Contaminated Objects (SCO) such as contaminated laboratory clothing or ores.
3. Type A Package: Designed to withstand normal conditions of air transport (water spray, free drop from 1.2 m, stacking, and penetration tests) without loss or dispersal of radioactive contents. Activity is strictly limited to $\le A_1$ or $\le A_2$.
4. Type B Package [Type B(U) / Type B(M)]: Designed to withstand severe hypothetical accident conditions (drop from 9 m onto unyielding surface, thermal test at 800°C for 30 minutes, 15 m water immersion test). Used for high-activity industrial sources (e.g., Cobalt-60, Iridium-192). Requires Unilateral B(U) or Multilateral B(M) competent authority approval.
5. Type C Package: Designed for high-activity air transport capable of withstanding extreme impact (90 m/s impact test) and prolonged thermal tests.

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Transport Index (TI) Calculation

The Transport Index (TI) is a single dimensionless number assigned to a Class 7 package, overpack, or freight container to provide radiation exposure control during transport.

Mathematical Formula for TI

$\text{TI} = \text{Maximum radiation dose rate in mSv/h at 1 meter (3.3 ft) from outer surface} \times 100$

(Alternatively, TI is equal to the maximum radiation dose rate in mrem/h at 1 meter). The value obtained must be rounded UP to the first decimal place (e.g., $0.12 \rightarrow 0.2$).

Calculation Example: If the maximum radiation level measured 1 meter away from a Type A package surface is 0.025 mSv/h (2.5 mrem/h): $\text{TI} = 0.025 \times 100 = 2.5$

Air Transport Limit: The maximum Transport Index permitted for any individual package carried on a passenger or cargo aircraft without Exclusive Use is 10.0.

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Class 7 Package Categorization & Labeling

Every Class 7 package (except Excepted Packages) must be assigned to one of three categories based on surface radiation levels and the Transport Index:

                               CLASS 7 CATEGORY SELECTION MATRIX

    Surface Radiation Level (mSv/h)
         ▲
   2.0   │─────────────────────────────────────────────────────────────► EXCLUSIVE USE ONLY
         │                                                            │
         │                                                            │  Category III-YELLOW
   0.5   │──────────────────────────────┬─────────────────────────────┤
         │                              │                             │
         │   Category II-YELLOW         │   Category III-YELLOW       │
  0.005  ├───┬──────────────────────────┴─────────────────────────────┤
         │ I-│
         └───┴──────────────────────────┬─────────────────────────────► Transport Index (TI)
             0                         1.0                           10.0

Note: If the surface radiation level exceeds 2.0 mSv/h (200 mrem/h) or if the TI exceeds 10.0, the package must be transported under Exclusive Use shipment conditions.