How far apart must two dangerous goods be segregated on a ship?
Segregation code from 49 CFR Table 176.83(b), matching IMDG Code 7.2.4 for classes 2 to 9 · container separation on closed-hold and hatchless container ships · same container · subsidiary hazards · Updated 29 October 2026
Published by ShipCalculators.com. Method checked against 49 CFR 176.83, Tables 176.83(b), (f) and (l)(3), 49 CFR 171.25 and 171.7 and IMDG Code Amendment 42-24, IMO Resolution MSC.556(108), cited by paragraph on 28 October 2026. How calculators are checked
Answer
Class 3 with a 6.1 subsidiary hazard against Division 5.1 is code 2, "separated from", in 49 CFR Table 176.83(b) and IMDG Code 7.2.4. Closed containers on deck of a closed-hold container ship need one container space, at least 6 m fore and aft or 2.5 m athwartships, no stacking without a deck between, and separate containers.
Segregation of dangerous goods is the minimum separation that 49 CFR 176.83 and IMDG Code chapter 7.2 require between incompatible goods on a ship, set by one of four terms: “away from”, “separated from”, “separated by a complete compartment or hold from” and “separated longitudinally by an intervening complete compartment or hold from”. Table 176.83(b) of 49 CFR gives the term for each pair of classes, or X where only the entry’s own codes apply, and Tables 176.83(f) and 176.83(l)(3) turn the term into container spaces and bulkheads.1 For classes 2 to 9 the codes are the same as IMDG Code 7.2.4.3
Find the segregation for two dangerous goods
Pick the dangerous goods in two containers, A and B, to see how far apart they must be stowed and whether they may share a container.
Start from an example pair
The class is column 3 of the 49 CFR 172.101 table or the dangerous goods declaration; the subsidiary hazard is the second label code in column 6. A container with fabric sides or top is open (176.2).
Code 2, Separated from
Your result
Separated from
Segregation code
Term
Separated from
Class 3 flammable liquid with a 6.1 subsidiary against Division 5.1 oxidizer is code 2. Closed v closed on deck, closed holds: fore and aft 1 space, 6 m; athwartships 1 space, 2.5 m; not in one container.
The ship
Point at or tap a cell to see whether B may go there. Full drawings
Table 176.83(b) of 49 CFR puts Class 3 flammable liquid against Division 5.1 oxidizer at 2, separated from. With the subsidiary hazards counted, the strictest cell is 3 against 5.1, code 2. IMDG Code 7.2.4 gives the same code.
On a container ship with closed holds, closed versus closed on deck, Table 176.83(f) asks for one container space fore and aft or one container space athwartships. A container space is at least 6 m fore and aft and 2.5 m athwartships (176.83(f)(4)). In the same vertical line: not in the same vertical line unless segregated by a deck.
The two may not share a container: 176.83(d) bars it wherever any segregation is required. Packed as break-bulk on deck, the same code would need 6 m (20 feet) horizontally under 176.83(c)(2).
Cite or share this calculation
ShipCalculators.com, “IMDG Segregation Table Calculator: Classes and Containers.” Method: Table 176.83(b) of 49 CFR with the subsidiary hazard rule of 176.83(a)(6), and Table 176.83(f). Inputs: Class 3 flammable liquid with a Division 6.1 subsidiary hazard against Division 5.1 oxidizer, in closed containers on deck on a container ship with closed holds. Result: code 2, separated from; fore and aft 1 space, 6 m, athwartships 1 space, 2.5 m. https://shipcalculators.com/calculators/imdg-segregation
The citation names ShipCalculators.com as publisher; copying it adds today's date.
Strictest of 2, 1 with X lowest: 2, separated from.
Table 176.83(f), requirement 2, closed versus closed, on deck: fore and aft “One container space”, athwartships “One container space”; 1 × 6 m = 6 m; 1 × 2.5 m = 2.5 m.
Vertical: “Not in the same vertical line unless segregated by a deck”.
Same container: not permitted, 176.83(d).
Drawings of the separation on board
The ship in three views
Schematic ship to scale in meters: holds two container spaces long, seven rows, three tiers in the hold and two on deck, each tier drawn 2.5 m high. A real ship’s holds, rows and tiers fall where its plan puts them.
Plan: where B may go from A
To scale: each box is one container space, 6 m fore and aft by 2.5 m athwartships (176.83(f)(4)). Under deck the holds are drawn two spaces long and the compartments two rows wide; a real ship's bulkheads fall where its plan puts them.
Elevation: the same vertical line
Table 176.83(b), classes 2 to 9
Ringed in red: the cell that decided the code. Dashed: the other pairings counted.
Every container pair and deck on this ship
How the code was decided
A against B: 3 v 5.12
A's subsidiary against B: 6.1 v 5.11
49 CFR and the IMDG Code for this pair
49 CFR
IMDG
Code
2
2
Athwartships
2.5 m
2.4 m
Same container
Not permitted
Not permitted
Class 3 flammable liquid with a 6.1 subsidiary against Division 5.1 oxidizer is code 2. Closed v closed on deck, closed holds: fore and aft 1 space, 6 m; athwartships 1 space, 2.5 m; not in one container.
Point at a cell or tap it to read whether B may go there and which rule decides it; with a keyboard, tab to a drawing and use the arrow keys.
Segregation in plain words
Look up the two classes in the segregation table and note the code, 1 to 4 or X. Do the same for any subsidiary hazard against the other goods, and keep the highest code. Then read the container table for the ship: code 2 between closed containers on deck means one container space between them, 6 m fore and aft or 2.5 m athwartships, which other cargo that is not incompatible with either may fill (176.83(a)(2)). Any code from 1 to 4 keeps the two out of the same container.
Formula, assumptions, and limits
Segregation under 49 CFR 176.83 is a lookup in two steps: the segregation table, Table 176.83(b), gives one of four terms or X for the pair of goods, and Table 176.83(f) or 176.83(l)(3) turns that term into a separation between their containers. All three tables used here are printed in 49 CFR 176.83, which is US federal text; the IMDG Code is referred to by paragraph number.
where pA and pB are the primary classes or divisions of goods A and B, sA and sB their single subsidiary hazards if they have one, and T(i,j) the cell of Table 176.83(b) for row i and column j. The order is X<1<2<3<4, so R is the strictest term any pairing produces. A term with no subsidiary hazard is left out.
The separation is then read from the container table and converted to meters where it is stated in container spaces:
dfadath=6m×nfa=2.5m×nath
where nfa and nath are the container spaces the table gives fore and aft and athwartships, and dfa and dath the minimum distances under 176.83(f)(4).
Derivation
Primary against primary: the cell of Table 176.83(b).
Subsidiary hazards: 176.83(a)(6) applies a subsidiary hazard’s segregation “when that segregation is more restrictive than that required by the primary hazard”, so each subsidiary is looked up against the other goods. An explosive subsidiary hazard takes the Division 1.4 row, except for organic peroxides, which take Division 1.3.
Same class: under 176.83(a)(8), goods of the same class may be stowed together without regard to the segregation their subsidiary hazards would require, provided they do not react dangerously. The calculator applies this only where both primaries are the same class or division and the reader confirms that no dangerous reaction is possible.
Ship: Table 176.83(f) for container ships with closed holds, or Table 176.83(l)(3) for hatchless ships, by the code, the pair of containers (closed or open), the deck and the direction.
Same container: 176.83(d) bars two goods “for which any segregation is required” from one cargo transport unit. The calculator allows the same container only where the code is X, and then only subject to the column 10B codes of both entries.
Assumptions
Each of the two goods has at most one subsidiary hazard, as the caption of Table 176.83(b) assumes (“a single secondary hazard label”). Two or more send the reader to the entry.
The subsidiary against subsidiary term is included. Neither 176.83 nor IMDG 7.2.3 states it in so many words; including it can only raise the result.
A closed container is one that totally encloses its contents with permanent structures; fabric sides or a fabric top make it open (49 CFR 176.2).
All bulkheads and decks are resistant to fire and liquid, as the note under both container tables requires.
The fore and aft figure and the athwartship figure are two separate distances, one along each line. The drawings mark the nearest permitted position along each line from container A.
Both figures sit under the tables’ “Horizontal” heading, so the drawings apply them in every tier on A’s side of the deck. A slot on the other side of the deck and outside A’s vertical line is left unmarked: the tables’ on-deck and under-deck columns each cover two containers on the same side, and the package rules of 176.83(c)(2)(iv) and (v) for one on deck and one below do not extend to containers.
Worked example
Methanol, UN1230, is Class 3 with a Division 6.1 subsidiary hazard in the international entry of the 172.101 table. It travels in a closed container on deck of a container ship with closed holds. Calcium hypochlorite, dry, UN1748, is Division 5.1 with no subsidiary hazard, in another closed container on deck.
Subsidiary 6.1 against 5.1: row 6.1, column 5.1 gives 1.
R=max{2,1}=2, “separated from”.
Table 176.83(f), requirement 2, closed versus closed, on deck: one container space fore and aft, at least 6×1=6 m, or one container space athwartships, at least 2.5×1=2.5 m. Vertically, not in the same vertical line unless segregated by a deck.
Same container: not permitted, because a segregation is required (176.83(d)).
Column 10B does not change the distances. UN1748 carries codes 4, 25, 52, 56, 58, 69 and 142: code 4 keeps combustible material out of the same cargo transport unit, which 176.83(d) already bars here, and codes 52, 56, 58 and 69 separate it from acids, ammonium compounds, cyanides and hydrogen peroxide, none of which is methanol. Methanol’s code 40 keeps it clear of living quarters.5
The same pair in open containers under deck needs one bulkhead fore and aft and one bulkhead athwartships.
Edge cases and limits
X. No general rule: the result reads “check column 10B”, never “no segregation” and never “prohibited”. Class 9 is X against everything.
Requirement 4. Athwartship separation is prohibited in both container tables, and only the fore and aft line counts. One above the other is prohibited for closed versus closed in Table 176.83(f), and for closed versus closed and closed versus open in Table 176.83(l)(3); the other vertical cells are blank.
Explosive subsidiary. In the 172.101 table the type B organic peroxides, UN3101, UN3102, UN3111 and UN3112, carry an explosive subsidiary hazard. They take the 1.3 row, which is code 4 against Class 3 where the peroxide’s own row gives 2. Any other goods with an explosive subsidiary hazard take the 1.4 row under 49 CFR and the 1.3 row under IMDG 7.2.3.3.
Two explosive hazards. If both goods carry an explosive hazard, the cell is the asterisk of Table 176.83(b), which sends the reader to 176.144 for Class 1. The calculator stops there.
Positions off both lines. Tables 176.83(f) and 176.83(l)(3), like IMDG 7.4.3, give a distance fore and aft and a distance athwartships, and say nothing of a container placed diagonally to A. The calculator marks only the two lines and leaves diagonal positions to the planner.
Blank cells. Table 176.83(l)(3) leaves the vertical cell blank for requirement 1 open versus open, for every pair under requirement 3 and for requirement 4 open versus open; Table 176.83(f) leaves it blank for requirement 4 closed versus open and open versus open. The calculator says so; for requirement 3 it shows the requirement 2 rule, “not in the same vertical line”, as the least a stricter term can need. In Table 176.83(l)(3), “otherwise as for open versus open” under requirement 1 leads to a blank cell, so closed on top of open is left unmarked there.
Regulatory basis
The class table, the container tables and the definitions are 49 CFR 176.83 as current on the eCFR on 26 October 2026, last changed in substance by PHMSA’s HM-215N final rule of 30 March 2017, which aligned the HMR with IMDG Amendment 38-16.7 49 CFR 171.7 incorporates IMDG Amendment 41-22, and 171.25(b)(2) lets a vessel shipment follow the stowage and segregation requirements of IMDG Part 7 in place of Part 176.2 IMDG Amendment 42-24, adopted by MSC.556(108) on 23 May 2024, is the edition in force from 1 January 2026.3
Common errors
Reading X as prohibited. X is the table handing over to the entry. Two goods that are X against each other may still need segregation under a column 10B code, and may share a container when none applies.
Treating “away from” as a separate hold. 176.83(c)(2)(ii) allows “away from” goods in the same compartment or hold with 3 m (10 feet) horizontal separation. On a container ship, closed containers that are “away from” each other may be stowed side by side.
Converting with the box length. A container space is the 6 m distance of 176.83(f)(4), not the outside length of a 20 ft container.
Ignoring the subsidiary hazard. A Class 3 liquid with a corrosive subsidiary is still separated from Division 5.1 by the Class 3 row, but a Division 6.1 poison with a Class 3 subsidiary moves from code 1 to code 2.
Carrying “away from” goods in one container on the IMDG exception. The competent authority approval of IMDG 7.3.4.1 is not in 49 CFR 176.83(d).
49 CFR Table 176.83(b) segregation table, classes 2 to 8
This is the segregation table, Table 176.83(b) of 49 CFR, for classes 2 to 8, read from the eCFR on 26 October 2026. Each row is goods A, each column goods B, and the table is symmetric. Class 9 is X against every class, so its row and column are left out. For classes 2 to 9 every cell gives the same value as IMDG Code 7.2.4 in Amendment 42-24.1,3
A \ B
2.1
2.2
2.3
3
4.1
4.2
4.3
5.1
5.2
6.1
6.2
7
8
2.1
X
X
X
2
1
2
2
2
2
X
4
2
1
2.2
X
X
X
1
X
1
X
X
1
X
2
1
X
2.3
X
X
X
2
X
2
X
X
2
X
2
1
X
3
2
1
2
X
X
2
2
2
2
X
3
2
X
4.1
1
X
X
X
X
1
X
1
2
X
3
2
1
4.2
2
1
2
2
1
X
1
2
2
1
3
2
1
4.3
2
X
X
2
X
1
X
2
2
X
2
2
1
5.1
2
X
X
2
1
2
2
X
2
1
3
1
2
5.2
2
1
2
2
2
2
2
2
X
1
3
2
2
6.1
X
X
X
X
X
1
X
1
1
X
1
X
X
6.2
4
2
2
3
3
3
2
3
3
1
X
3
3
7
2
1
1
2
2
2
2
1
2
X
3
X
2
8
1
X
X
X
1
1
1
2
2
X
3
2
X
The table’s own legend: 1 “Away from”, 2 “Separated from”, 3 “Separated by a complete compartment or hold from”, 4 “Separated longitudinally by an intervening complete compartment or hold from”, X “The segregation, if any, is shown in the § 172.101 table”. Division 6.2 infectious substances carry the strictest row: code 3 or 4 against eight of the thirteen other classes.
Segregation terms in meters for packages
49 CFR 176.83(c)(2) sets each term for packages in conventional stowage as a distance: on deck, 3 m for “away from”, 6 m for “separated from”, 12 m for code 3 and 24 m longitudinally for code 4. The container tables build on these definitions.1
Code
Term
On deck
Under deck
1
Away from
3 m (10 feet) horizontally
Same compartment or hold, 3 m (10 feet) apart
2
Separated from
6 m (20 feet) horizontally
Different compartments or holds; one above the other only through a deck resistant to fire and liquid
3
Separated by a complete compartment or hold from
12 m (39 feet) horizontally
A complete compartment or hold between them, vertically or horizontally; only longitudinally where the decks are not resistant to fire and liquid
4
Separated longitudinally by an intervening complete compartment or hold from
24 m (79 feet) longitudinally
An intervening complete compartment or hold, longitudinally; vertical separation alone does not meet it. One under deck and one on deck: 24 m (79 feet) longitudinally, including a complete compartment
Container ships with closed holds and hatchless ships
Between containers, 49 CFR asks for anything from no horizontal restriction, for closed containers “away from” each other, to four container spaces (at least 24 m) fore and aft under requirement 4. Table 176.83(f) covers container ships whose holds are closed by hatch covers, and Table 176.83(l)(3) hatchless ships, which have no hatch covers.1 Both count separation in container spaces and bulkheads. In both, closed containers that are “away from” each other have no horizontal restriction, and one may sit on top of the other.
The hatchless table adds “not in or above same hold” to every on-deck figure for open containers under requirement 2, and for all pairs on deck under requirements 3 and 4. Requirement 4 on a hatchless ship is stated as a minimum horizontal distance of 24 m where the closed-hold table says four container spaces; the minimum is the same.
Under deck on a closed-hold ship, requirement 4 between closed containers needs “one bulkhead and four container spaces”, with each container at least 6 m from the bulkhead between them.
Where 49 CFR and the IMDG Code differ
49 CFR 176.83 and IMDG Code Amendment 42-24 give the same code for classes 2 to 9 without an explosive subsidiary hazard, and part in five places that change a result. A US vessel shipment may follow IMDG Part 7 instead of 49 CFR Part 176 (49 CFR 171.25(b)(2)), in the edition 49 CFR 171.7 incorporates, Amendment 41-22, so a ship’s stowage plan may follow either book.2
Point
49 CFR 176.83
IMDG Code Amendment 42-24
Division 1.6
Grouped with 1.4
Grouped with 1.3 (7.2.4)
Explosive subsidiary hazard
Division 1.4 row; organic peroxides 1.3 ((a)(6))
Division 1.3 row (7.2.3.3)
Container space athwartships
2.5 m (8 feet) ((f)(4))
2.4 m (7.4.3.1.1)
“Away from” goods in one container
Not permitted ((d))
Permitted with competent authority approval (7.3.4.1)
Class 8 acids and alkalis
No exception in 176.83
May share a unit, up to 30 L or 30 kg per package, under 7.2.6.5
The entry codes differ in form too. X in 49 CFR points to the numbered stowage codes of column 10B, set out in 176.84; X in the IMDG Code points to the SG codes in column 16b of the Dangerous Goods List.5 PHMSA’s HM-215R proposal of 10 February 2026 would rewrite only paragraph (a)(8) of 176.83, and has not been adopted.8 Its HM-215S proposal of 27 October 2026 would replace the IMDG edition 176.83 refers to with Amendment 43-26, which becomes mandatory on 1 January 2027; comments close on 28 December 2026.10
Goods outside this calculator
This calculator does not cover Class 1 as a primary hazard, the column 10B entry codes, the Class 7 distances of 49 CFR 176.708, or ro-ro, barge and break-bulk stowage.
Class 1 explosives as primary hazard. Segregation within Class 1 uses compatibility groups under 49 CFR 176.144.4 In the 49 CFR table an X there means the two groups may not be stowed together; in IMDG 7.2.7.1.4 an X marks mixed stowage that is permitted. With X meaning opposite things in the two books, this page leaves Class 1 to the source text.
Column 10B codes and segregation groups. A code such as “stow away from acids” in the 172.101 table applies on top of the class result, to every substance in the group that 49 CFR 176.83(m) imports from IMDG 3.1.4.6
Class 7. Table 176.83(b) gives the class result; the distances from crew spaces and undeveloped film are in 176.708.9
Ro-ro, barges and breakbulk stowage plans. Table 176.83(g) for trailerships and trainships, and the barge rules of 176.83(h) to (j), use other distances.
Limits of this segregation check
Class 1 explosives as a primary hazard are not covered: segregation within Class 1 and against Class 1 follows the compatibility groups of 49 CFR 176.144 and IMDG 7.2.7, where an X means opposite things in the two books.4
The column 10B codes of the 172.101 table and the segregation groups imported by 176.83(m) are not applied. Where the class result is X, or an entry names a group such as acids, read the entry.5,6
One subsidiary hazard per goods, as Table 176.83(b) assumes. Entries with two or more go to the entry codes.
Container ships only. Ro-ro decks (Table 176.83(g)), barges and conventional break-bulk stowage use other distances, and Class 7 adds the distances of 176.708.9
The answer follows 49 CFR. A ship stowing under IMDG Part 7 gets a different result for Division 1.6, explosive subsidiary hazards, the 2.4 m athwartship space, the same-container exception and Class 8 acids and alkalis.2,3
Regulatory basis
The tables are 49 CFR 176.83 as current on the eCFR on 26 October 2026, last changed in substance on 30 March 2017.1,7 49 CFR 171.7 incorporates IMDG Amendment 41-22, and 171.25(b)(2) lets a vessel shipment follow IMDG Part 7 instead.2 IMDG Amendment 42-24, adopted by MSC.556(108), is in force from 1 January 2026.3 PHMSA’s HM-215S proposal of 27 October 2026 would move the edition 176.83 refers to on to Amendment 43-26.10
Codes
1 away from, 2 separated from, 3 separated by a complete compartment or hold from, 4 separated longitudinally by an intervening complete compartment or hold from, X see the entry; Table 176.83(b)1
Subsidiary hazard
Applied when stricter than the primary, 176.83(a)(6); explosive subsidiary as Division 1.4, organic peroxides as 1.31
Same class
Subsidiary segregation may be set aside if no dangerous reaction, 176.83(a)(8)1
Container space
6 m (20 feet) fore and aft, 2.5 m (8 feet) athwartships, 176.83(f)(4); IMDG 7.4.3.1.1 uses 2.4 m1,3
Same container
Not where any segregation is required, 176.83(d); IMDG 7.3.4.1 allows “away from” goods with competent authority approval1,3
Entry codes
Column 10B of the 172.101 table, codes in 176.84; IMDG column 16b SG codes5,6
Frequently Asked Questions (FAQs)
What do segregation codes 1, 2, 3, 4 and X mean?
In Table 176.83(b) of 49 CFR, and in IMDG Code 7.2.4, 1 is "away from", 2 "separated from", 3 "separated by a complete compartment or hold from" and 4 "separated longitudinally by an intervening complete compartment or hold from". X means the table sets no general rule and any segregation is in the particular entry: column 10B of the 172.101 Hazardous Materials Table in 49 CFR, column 16b of the Dangerous Goods List in the IMDG Code.
Does X in the segregation table mean the goods cannot be stowed together?
No. X means the class table sets no general requirement, and the entries for the two goods must be checked for a particular one. Two Class 3 flammable liquids are X against each other, and may share a container unless a column 10B code of either entry bars it; an entry whose column 10B code says "stow away from" a class or group still applies.
How far apart must Class 3 and Class 5.1 containers be?
Class 3 against Division 5.1 is code 2, "separated from". For closed containers on deck of a container ship with closed holds, Table 176.83(f) of 49 CFR asks for one container space fore and aft (at least 6 m) or athwartships (at least 2.5 m), and not in the same vertical line unless a deck separates them. Open containers on deck need two container spaces athwartships.
What is a container space?
A distance, not a slot. Under 49 CFR 176.83(f)(4) it is not less than 6 m (20 feet) fore and aft or not less than 2.5 m (8 feet) athwartships. IMDG Code 7.4.3.1.1 uses 6 m and 2.4 m.
Can two dangerous goods that need segregation go in the same container?
Not under 49 CFR: 176.83(d) says two hazardous materials for which any segregation is required may not be stowed in the same cargo transport unit. IMDG Code 7.3.4.1 adds one exception: goods segregated "away from" each other may share a unit with the approval of the competent authority.
How do you read the segregation table?
Find the row for one goods' class or division and the column for the other's. Table 176.83(b) of 49 CFR is symmetric, so either order gives the same cell. Do the same for any subsidiary hazard against the other goods and keep the strictest code, with X lowest and 4 highest (176.83(a)(6)). Then read column 10B of both entries in the 172.101 table, which can add a requirement on top.
What are segregation groups, such as acids and alkalis?
Under 49 CFR 176.83(m), materials with similar chemical properties are grouped together in segregation groups, such as acids, chlorates and permanganates, whose members include the substances identified in section 3.1.4 of the IMDG Code. When column 10B of the 172.101 table refers to a numbered provision of 176.84(b) such as "Stow 'away from' acids", that requirement applies to all materials allocated to the group, on top of the class result from Table 176.83(b).
Do subsidiary hazards count in segregation?
Yes. 49 CFR 176.83(a)(6) applies the segregation of a subsidiary hazard label when it is stricter than that of the primary hazard, and the caption of Table 176.83(b) says segregation must take account of a single secondary hazard label. A Division 6.1 poison with a Class 3 subsidiary hazard is "separated from" Division 5.1, because Class 3 against 5.1 is code 2.
Is the 49 CFR segregation table the same as the IMDG Code table?
For classes 2 to 9 it gives the same code in every cell as IMDG Code 7.2.4 in Amendment 42-24. The two differ for Division 1.6, for goods with an explosive subsidiary hazard, for the athwartship container space (2.5 m against 2.4 m), for the same-container exception and for Class 8 acids and alkalis. 49 CFR 171.7 incorporates IMDG Amendment 41-22, and under 49 CFR 171.25(b)(2) a US vessel shipment may follow Part 7 of that edition instead of Part 176.
How to use this calculator
Pick the primary class or division of the first goods, from column 3 of the 49 CFR 172.101 Hazardous Materials Table or the dangerous goods declaration.
Pick its subsidiary hazard, if the entry has one, from the label codes in column 6. An explosive subsidiary hazard is entered as 1.
Pick the class and any subsidiary hazard of the second goods the same way.
If both goods have the same primary class or division, say whether they could react dangerously together. If they cannot, 176.83(a)(8) lets the subsidiary hazards be set aside.
Pick the ship (closed holds or hatchless), whether each container is closed or open, and whether the stow is on deck or under deck.
Read the segregation code and its term, the vertical rule, the separation fore and aft and athwartships in container spaces, bulkheads or meters, and whether the two may share a container. Where the code is X, check column 10B of both entries.
Test cases this calculator passes
Every build of this site runs these cases through the calculator above and stops the release if any figure moves outside its tolerance. Load a case to put its inputs into the calculator.
Inputs
Expected result
Traced to
Load
Default: Class 3 with a 6.1 subsidiary (methanol, UN1230) against Division 5.1 (calcium hypochlorite, UN1748), closed containers on deck, closed holds
Segregation code: 2Term: Separated fromSame vertical line: Deck betweenFore and aft: 1 space, 6 mAthwartships: 1 space, 2.5 mSame container: Not permittedPackages on deck: 6 m apart
Table 176.83(b): T(3, 5.1) = 2, T(6.1, 5.1) = 1, max 2 (176.83(a)(6)). Table 176.83(f), requirement 2, closed v closed, on deck: one container space fore and aft and athwartships; vertical not in the same vertical line unless segregated by a deck. 176.83(f)(4): 6 m and 2.5 m. 176.83(d): no shared CTU. 176.83(c)(2)(iii): 6 m on deck.
Class 8 against Division 4.3, closed containers on deck
Segregation code: 1Term: Away fromSame vertical line: May stackFore and aft: No restrictionAthwartships: No restrictionSame container: Not permittedPackages on deck: 3 m apart
Table 176.83(b): T(8, 4.3) = 1, away from. Table 176.83(f), requirement 1, closed v closed: one on top of the other permitted; no restriction fore and aft or athwartships. 176.83(d): no shared CTU; IMDG 7.3.4.1 allows one with competent authority approval.
Segregation code: XTerm: No general rule: see the entriesSame vertical line: See 10BFore and aft: See 10BAthwartships: See 10BSame container: If 10B allowsPackages on deck: See 10B
Table 176.83(b): T(2.1, 6.1) = X, 'The segregation, if any, is shown in the 172.101 table'. No general requirement; column 10B of both entries decides, including whether they may share a CTU.
Division 2.1 against Division 6.2, closed containers under deck: code 4
Segregation code: 4Term: Separated longitudinally by an intervening complete compartment or hold fromSame vertical line: ProhibitedFore and aft: 1 bulkhead + 4 spacesAthwartships: ProhibitedSame container: Not permittedPackages on deck: 24 m apart
Table 176.83(b): T(2.1, 6.2) = 4. Table 176.83(f), requirement 4, closed v closed, under deck: 'One bulkhead and four container spaces*', containers not less than 6 m from the intervening bulkhead; athwartships prohibited; vertical prohibited. 176.83(c)(2)(v): 24 m.
Segregation code: 2Term: Separated fromSame vertical line: Deck betweenFore and aft: 1 bulkheadAthwartships: 1 bulkheadSame container: Not permittedPackages on deck: 6 m apart
Table 176.83(f), requirement 2, open v open, under deck: one bulkhead fore and aft and athwartships; vertical not in the same vertical line unless segregated by a deck.
Default goods in open containers on deck of a hatchless ship
Segregation code: 2Term: Separated fromSame vertical line: Not same lineFore and aft: 1 space, 6 mAthwartships: 2 spaces, 5 mSame container: Not permittedPackages on deck: 6 m apart
Table 176.83(l)(3), requirement 2, open v open, on deck: 'One container space and not in or above same hold' fore and aft; 'Two container spaces and not in or above same hold' athwartships (2 x 2.5 m = 5 m); vertical not in same vertical line.
Division 6.2 against Class 3, closed containers on deck of a hatchless ship
Segregation code: 3Term: Separated by a complete compartment or hold fromSame vertical line: Not same lineFore and aft: 1 space, 6 mAthwartships: 2 spaces, 5 mSame container: Not permittedPackages on deck: 12 m apart
Table 176.83(b): T(6.2, 3) = 3. Table 176.83(l)(3), requirement 3, closed v closed, on deck: one container space fore and aft and two athwartships, each 'and not in or above same hold'. Vertical cell blank in the CFR table; shown as for requirement 2, not in the same vertical line.
Division 5.2 with an explosive subsidiary (organic peroxide type B, UN3101) against Class 3
Segregation code: 4Term: Separated longitudinally by an intervening complete compartment or hold fromSame vertical line: ProhibitedFore and aft: 4 spaces, 24 mAthwartships: ProhibitedSame container: Not permittedPackages on deck: 24 m apart
172.101: UN3101 labels 5.2, 1. 176.83(a)(6): explosive subsidiary of an organic peroxide takes Division 1.3. T(5.2, 3) = 2, T(1.3, 3) = 4, max 4. Table 176.83(f), requirement 4, closed v closed, on deck: four container spaces fore and aft (24 m), athwartships prohibited. IMDG 7.2.3.3 also 1.3: code 4.
Division 5.1 with a Class 8 subsidiary against Division 5.1, no dangerous reaction
Segregation code: XTerm: No general rule: see the entriesSame vertical line: See 10BFore and aft: See 10BAthwartships: See 10BSame container: If 10B allowsPackages on deck: See 10B
176.83(a)(8): same class, subsidiary segregation set aside when no dangerous reaction. T(5.1, 5.1) = X.
Two organic peroxides type B (Division 5.2 with an explosive subsidiary each, such as UN3101 and UN3111) that cannot react dangerously, closed containers on deck, closed holds
Segregation code: XTerm: No general rule: see the entriesSame container: If 10B allows
Same division and no dangerous reaction: 176.83(a)(8) sets the subsidiary hazards aside, so only T(5.2, 5.2) = X counts in Table 176.83(b).
Lithium batteries are Class 9, which is X against every class in Table 176.83(b); the lithium battery shipping calculator finds their UN number, packing instruction and marks.
Change log
Each change to the method, a coefficient or a test case, with the date it reached this page.
Rebuilt on 49 CFR Tables 176.83(b), (f) and (l)(3), with 13 test cases. The earlier page described X as a prohibition, “away from” as a different hold and requirement 4 under deck as two intervening holds; all three were wrong under both 49 CFR and the IMDG Code.
Who publishes this calculator and how it is checked
Publisher
ShipCalculators.com, an independent site of maritime calculators.
How it is checked
Each figure is traced to the instrument that sets it, and the test cases on this page run against the calculator code on every build; a build that moves one of them does not deploy. Last method check: 28 October 2026.
What it is not
Not a stowage plan or a segregation check by the master or the carrier: the entries' own codes, the ship's Document of Compliance for dangerous goods and the carrier's rules can each add to this result.