"What are the no-decompression limits for air diving?"

"Per USN Table 9-7 (Revision 7), no-decompression limits for air diving range from Unlimited at 10–20 FSW down to 5 minutes at 190 FSW. At 60 FSW the NDL is 63 minutes; at 100 FSW it is 25 minutes; at 130 FSW it is 12 minutes. These limits apply to first dives (no residual nitrogen). For repetitive dives, calculate Equivalent Single Dive Time using Table 9-8 before applying the NDL."

"What is the NDL at 60 feet on air?"

"Per USN Table 9-7, the no-decompression limit at 60 FSW on air is 63 minutes for a Group A diver (no prior repetitive dives within the 12-hour repetitive interval). The maximum achievable repetitive group at 60 FSW is Group K."

"What is the NDL at 100 feet on air?"

"Per USN Table 9-7, the no-decompression limit at 100 FSW on air is 25 minutes for a Group A diver. At 100 FSW the maximum achievable group is Group H. Decompression stops per Table 9-9 are required if this limit is exceeded."

"What is the NDL at 40 feet on air?"

"Per USN Table 9-7, the no-decompression limit at 40 FSW on air is 163 minutes for a Group A diver. For more precise planning at depths 38–42 FSW, use Table 2A-1 which provides NDLs in 1-foot increments (e.g., 184 min at 38 FSW, 155 min at 41 FSW)."

"What does an asterisk (*) mean in the USN NDL table?"

"An asterisk (*) in Table 9-7 indicates the highest repetitive group achievable at that depth, regardless of additional bottom time. For example, at 10 FSW the asterisk appears in column F — no matter how long you stay at 10 FSW, you cannot accumulate more nitrogen than Group F represents. The No-Stop Limit is listed as Unlimited for these shallow depths."

"What is Table 2A-1 and how is it different from Table 9-7?"

"Table 2A-1 is the Shallow Water Air No-Decompression Limits table from the USN Diving Manual Rev 7. Where Table 9-7 lists depths in standard increments (30, 35, 40 FSW), Table 2A-1 provides NDLs and repetitive groups for every foot from 30 to 50 FSW. This allows precise planning for dives at non-standard depths like 37 FSW or 43 FSW within the shallow water range."

USN No-Decompression Limits — Table 9-7 & 2A-1 (Air Diving)

Source: SS521-AG-PRO-010, U.S. Navy Diving Manual, Revision 7, 01 December 2016

CRITICAL WARNING: These tables are transcribed from the official USN Diving Manual Revision 7. They must be verified against the original NAVSEA publication before operational use. Transcription errors, however unlikely, could be fatal.

Opens print dialog — choose "Save as PDF" to download

Interactive NDL Lookup — Tables 9-7 & 9-8

Enter depth and bottom time to instantly find your no-decompression status and repetitive group. Enter a surface interval for repetitive dive calculations.

Enter depth and bottom time to find your no-decompression status and repetitive group (Table 9-7).

Depth (FSW)

Bottom Time (min)

Plan a second dive using Table 9-8. Enter your post-dive group, surface interval, and next dive depth.

Step 1 — Surface interval credit (Table 9-8, Part 1)

Post-Dive Group

Surface Interval

Next Depth (FSW)

Verify before operational use. These values are transcribed from USN Diving Manual Rev 7 (SS521-AG-PRO-010). Cross-reference with the official NAVSEA publication before any dive. Transcription errors, however unlikely, can be fatal.

Table 9-7. No-Decompression Limits and Repetitive Group Designators

For standard depths 10–190 FSW. The No-Stop Limit column shows the maximum bottom time (minutes) without required decompression stops. The lettered columns show the repetitive group accumulated at that bottom time.

* = Highest repetitive group achievable at this depth regardless of bottom time. Blank cells = Group not achievable at this depth.

Depth (fsw)	No-Stop Limit (min)	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	Z
10	Unlimited	57	101	158	245	426	*
15	Unlimited	36	60	88	121	163	217	297	449	*
20	Unlimited	26	43	61	82	106	133	165	205	256	330	461	*
25	1102	20	33	47	62	78	97	117	140	166	198	236	285	354	469	992	1102
30	371	17	27	38	50	62	76	91	107	125	145	167	193	223	260	307	371
35	232	14	23	32	42	52	63	74	87	100	115	131	148	168	190	215	232
40	163	12	20	27	36	44	53	63	73	84	95	108	121	135	151	163
45	125	11	17	24	31	39	46	55	63	72	82	92	102	114	125
50	92	9	15	21	28	34	41	48	56	63	71	80	89	92
55	74	8	14	19	25	31	37	43	50	56	63	71	74
60	63	7	12	17	22	28	33	39	45	51	57	63
70	48	6	10	14	19	23	28	32	37	42	47	48
80	39	5	9	12	16	20	24	28	32	36	39
90	33	4	7	11	14	17	21	24	28	31	33
100	25	4	6	9	12	15	18	21	25
110	20	3	6	8	11	14	16	19	20
120	15	3	5	7	10	12	15
130	12	2	4	6	9	11	12
140	10	2	4	6	8	10
150	8		3	5	7	8
160	7		3	5	6	7
170	6			4	6
180	6			4	5	6
190	5			3	5

Dives to 200 FSW and deeper have no no-decompression option — decompression stops are mandatory. Use Table 9-9 for required decompression schedules.

Table 2A-1. Shallow Water NDL — 30 to 50 FSW (1-Foot Increments)

For precise planning at non-standard depths within the 30–50 FSW range. Same repetitive group designators as Table 9-7.

Blank cells = Group not achievable at this depth.

Depth (fsw)	No-Stop Limit (min)	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	Z
30	371	17	27	38	50	62	76	91	107	125	145	167	193	223	260	307	371
31	334	16	26	37	48	60	73	87	102	119	138	158	182	209	242	282	334
32	304	15	25	35	46	58	70	83	98	114	131	150	172	197	226	261	304
33	281	15	24	34	45	56	67	80	94	109	125	143	163	186	212	243	281
34	256	14	23	33	43	54	65	77	90	104	120	137	155	176	200	228	256
35	232	14	23	32	42	52	63	74	87	100	115	131	148	168	190	215	232
36	212	14	22	31	40	50	61	72	84	97	110	125	142	160	180	204	212
37	197	13	21	30	39	49	59	69	81	93	106	120	136	153	172	193	197
38	184	13	21	29	38	47	57	67	78	90	102	116	131	147	164	184
39	173	12	20	28	37	46	55	65	76	87	99	112	126	141	157	173
40	163	12	20	27	36	44	53	63	73	84	95	108	121	135	151	163
41	155	12	19	27	35	43	52	61	71	81	92	104	117	130	145	155
42	147	11	19	26	34	42	50	59	69	79	89	101	113	126	140	147
43	140	11	18	25	33	41	49	58	67	76	87	98	109	122	135	140
44	134	11	18	25	32	40	48	56	65	74	84	95	106	118	130	134
45	125	11	17	24	31	39	46	55	63	72	82	92	102	114	125
46	116	10	17	23	30	38	45	53	61	70	79	89	99	110	116
47	109	10	16	23	30	37	44	52	60	68	77	87	97	107	109
48	102	10	16	22	29	36	43	51	58	67	75	84	94	102
49	97	10	16	22	28	35	42	49	57	65	73	82	91	97
50	92	9	15	21	28	34	41	48	56	63	71	80	89	92

For residual nitrogen times at these depths in 1-foot increments, see Table 2A-2 on the full air tables page.

How to Use These Tables

Single Dive (no prior dives within 12 hours)

Find your planned depth in the Depth column
Read across to find the No-Stop Limit — your maximum bottom time
Find the column matching your actual bottom time to read your Repetitive Group on surfacing
If your planned bottom time exceeds the No-Stop Limit, decompression stops are required — use Table 9-9

Repetitive Dive (prior dive within 12 hours)

Note your Repetitive Group from the previous dive (Table 9-7)
Find your surface interval in Table 9-8 Part 1 to determine your new group
Use Table 9-8 Part 2 with your new group and next dive depth → Residual Nitrogen Time (RNT)
Add RNT to planned bottom time → Equivalent Single Dive Time (ESDT)
If ESDT exceeds the NDL, use Table 9-9 for the required decompression schedule

Use the interactive tool at the top of this page to perform repetitive dive calculations automatically.

USN Air Decompression Table (Table 9-9) — Required stops when the NDL is exceeded; also contains Tables 9-7, 9-8, 9-5, 9-6, 2A-1, and 2A-2
USN HeO2 Dive Tables (Table 12-4) — Helium-oxygen mixed gas decompression
Dive Planning & Risk Assessment
Dive Logs & Operational Records

Depth (fsw)	No-Stop Limit (min)	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	Z
30	371	17	27	38	50	62	76	91	107	125	145	167	193	223	260	307	371
31	334	16	26	37	48	60	73	87	102	119	138	158	182	209	242	282	334
32	304	15	25	35	46	58	70	83	98	114	131	150	172	197	226	261	304
33	281	15	24	34	45	56	67	80	94	109	125	143	163	186	212	243	281
34	256	14	23	33	43	54	65	77	90	104	120	137	155	176	200	228	256
35	232	14	23	32	42	52	63	74	87	100	115	131	148	168	190	215	232
36	212	14	22	31	40	50	61	72	84	97	110	125	142	160	180	204	212
37	197	13	21	30	39	49	59	69	81	93	106	120	136	153	172	193	197
38	184	13	21	29	38	47	57	67	78	90	102	116	131	147	164	184
39	173	12	20	28	37	46	55	65	76	87	99	112	126	141	157	173
40	163	12	20	27	36	44	53	63	73	84	95	108	121	135	151	163
41	155	12	19	27	35	43	52	61	71	81	92	104	117	130	145	155
42	147	11	19	26	34	42	50	59	69	79	89	101	113	126	140	147
43	140	11	18	25	33	41	49	58	67	76	87	98	109	122	135	140
44	134	11	18	25	32	40	48	56	65	74	84	95	106	118	130	134
45	125	11	17	24	31	39	46	55	63	72	82	92	102	114	125
46	116	10	17	23	30	38	45	53	61	70	79	89	99	110	116
47	109	10	16	23	30	37	44	52	60	68	77	87	97	107	109
48	102	10	16	22	29	36	43	51	58	67	75	84	94	102
49	97	10	16	22	28	35	42	49	57	65	73	82	91	97
50	92	9	15	21	28	34	41	48	56	63	71	80	89	92

Depth (fsw)	No-Stop Limit (min)	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	Z
30	371	17	27	38	50	62	76	91	107	125	145	167	193	223	260	307	371
31	334	16	26	37	48	60	73	87	102	119	138	158	182	209	242	282	334
32	304	15	25	35	46	58	70	83	98	114	131	150	172	197	226	261	304
33	281	15	24	34	45	56	67	80	94	109	125	143	163	186	212	243	281
34	256	14	23	33	43	54	65	77	90	104	120	137	155	176	200	228	256
35	232	14	23	32	42	52	63	74	87	100	115	131	148	168	190	215	232
36	212	14	22	31	40	50	61	72	84	97	110	125	142	160	180	204	212
37	197	13	21	30	39	49	59	69	81	93	106	120	136	153	172	193	197
38	184	13	21	29	38	47	57	67	78	90	102	116	131	147	164	184
39	173	12	20	28	37	46	55	65	76	87	99	112	126	141	157	173
40	163	12	20	27	36	44	53	63	73	84	95	108	121	135	151	163
41	155	12	19	27	35	43	52	61	71	81	92	104	117	130	145	155
42	147	11	19	26	34	42	50	59	69	79	89	101	113	126	140	147
43	140	11	18	25	33	41	49	58	67	76	87	98	109	122	135	140
44	134	11	18	25	32	40	48	56	65	74	84	95	106	118	130	134
45	125	11	17	24	31	39	46	55	63	72	82	92	102	114	125
46	116	10	17	23	30	38	45	53	61	70	79	89	99	110	116
47	109	10	16	23	30	37	44	52	60	68	77	87	97	107	109
48	102	10	16	22	29	36	43	51	58	67	75	84	94	102
49	97	10	16	22	28	35	42	49	57	65	73	82	91	97
50	92	9	15	21	28	34	41	48	56	63	71	80	89	92

Interactive NDL Lookup — Tables 9-7 & 9-8#

Table 9-7. No-Decompression Limits and Repetitive Group Designators#

Table 2A-1. Shallow Water NDL — 30 to 50 FSW (1-Foot Increments)#

How to Use These Tables#

Single Dive (no prior dives within 12 hours)#

Repetitive Dive (prior dive within 12 hours)#

Related Tables#