###### Editorial Note on [Part 173](/current/title-49/part-173?toc=1)

#### Editorial Note:

Nomenclature changes to part 173 appear at [70 FR 56098](https://www.federalregister.gov/citation/70-FR-56098), Sept. 23, 2005.

#### § 173.52 Classification codes and compatibility groups of explosives.

(a) The classification code for an explosive, which is assigned by the Associate Administrator in accordance with this subpart, consists of the division number followed by the compatibility group letter. Compatibility group letters are used to specify the controls for the transportation, and storage related thereto, of explosives and to prevent an increase in hazard that might result if certain types of explosives were stored or transported together. Transportation compatibility requirements for carriers are prescribed in [§§ 174.81](/on/2024-09-24/title-49/section-174.81), [175.78](/on/2024-09-24/title-49/section-175.78). 176.83 and 177.848 of this subchapter for transportation by rail, air, vessel, and public highway, respectively, and storage incidental thereto.

(b) Compatibility groups and classification codes for the various types of explosives are set forth in the following tables. Table 1 sets forth compatibility groups and classification codes for substances and articles described in the first column of table 1. Table 2 shows the number of classification codes that are possible within each explosive division. Altogether, there are 35 possible classification codes for explosives.

Table 1—Classification Codes

| Description of substances or article to be classified | Compatibility group | Classification code |
| --- | --- | --- |
| Primary explosive substance | A | 1.1A |
| Article containing a primary explosive substance and not containing two or more effective protective features. Some articles, such as detonators for blasting, detonator assemblies for blasting and primers, cap-type, are included, even though they do not contain primary explosives. | B | 1.1B 1.2B 1.4B |
| Propellant explosive substance or other deflagrating explosive substance or article containing such explosive substance | C | 1.1C 1.2C 1.3C 1.4C |
| Secondary detonating explosive substance or black powder or article containing a secondary detonating explosive substance, in each case without means of initiation and without a propelling charge, or article containing a primary explosive substance and containing two or more effective protective features | D | 1.1D 1.2D 1.4D 1.5D |
| Article containing a secondary detonating explosive substance, without means of initiation, with a propelling charge (other than one containing flammable liquid or gel or hypergolic liquid) | E | 1.1E 1.2E 1.4E |
| Article containing a secondary detonating explosive substance with its means of initiation, with a propelling charge (other than one containing flammable liquid or gel or hypergolic liquid) or without a propelling charge | F | 1.1F 1.2F 1.3F 1.4F |
| Pyrotechnic substance or article containing a pyrotechnic substance, or article containing both an explosive substance and an illuminating, incendiary, tear-producing or smoke-producing substance (other than a water-activated article or one containing white phosphorus, phosphide or flammable liquid or gel or hypergolic liquid) | G | 1.1G 1.2G 1.3G 1.4G |
| Article containing both an explosive substance and white phosphorus | H | 1.2H 1.3H |
| Article containing both an explosive substance and flammable liquid or gel | J | 1.1J 1.2J 1.3J |
| Article containing both an explosive substance and a toxic chemical agent | K | 1.2K 1.3K |
| Explosive substance or article containing an explosive substance and presenting a special risk (e.g., due to water-activation or presence of hybergolic liquids, phosphides or pyrophoric substances) needing isolation of each type | L | 1.1L 1.2L 1.3L |
| Articles predominantly containing extremely insensitive substances | N | 1.6N |
| Substance or article so packed or designed that any hazardous effects arising from accidental functioning are limited to the extent that they do not significantly hinder or prohibit fire fighting or other emergency response efforts in the immediate vicinity of the package | S | 1.4S |

Table 2—Scheme of Classification of Explosives, Combination of Hazard Division with Compatibility Group

| Hazard division | Compatibility group | | | | | | | | | | | | | |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| A | B | C | D | E | F | G | H | J | K | L | N | S | A-S |
| 1.1 | 1.1A | 1.1B | 1.1C | 1.1D | 1.1E | 1.1F | 1.1G | | 1.1J | | 1.1L | | | 9 |
| 1.2 | | 1.2B | 1.2C | 1.2D | 1.2E | 1.2F | 1.2G | 1.2H | 1.2J | 1.2K | 1.2L | | | 10 |
| 1.3 | | | 1.3C | | | 1.3F | 1.3G | 1.3H | 1.3J | 1.3K | 1.3L | | | 7 |
| 1.4 | | 1.4B | 1.4C | 1.4D | 1.4E | 1.4F | 1.4G | | | | | | 1.4S | 7 |
| 1.5 | | | | 1.5D | | | | | | | | | | 1 |
| 1.6 | | | | | | | | | | | | 1.6N | | 1 |
| Total | 1 | 3 | 4 | 4 | 3 | 4 | 4 | 2 | 3 | 2 | 3 | 1 | 1 | 35 |

[Amdt. 173-224, [55 FR 52617](https://www.federalregister.gov/citation/55-FR-52617), Dec. 21, 1990, as amended by Amdt. 173-241, [59 FR 67492](https://www.federalregister.gov/citation/59-FR-67492), Dec. 29, 1994; [64 FR 51918](https://www.federalregister.gov/citation/64-FR-51918), Sept. 27, 1999; [66 FR 45379](https://www.federalregister.gov/citation/66-FR-45379), Aug. 28, 2001; [76 FR 56315](https://www.federalregister.gov/citation/76-FR-56315), Sept. 13, 2011; [78 FR 1074](https://www.federalregister.gov/citation/78-FR-1074), Jan. 7, 2013; [82 FR 15876](https://www.federalregister.gov/citation/82-FR-15876), Mar. 30, 2017]