ISO 7010:2019 / ISO 3864-1
ISO P051 No sub-aqua diving Sign
ISO P051 No sub-aqua diving Sign means the P051 sign prohibits sub-aqua diving — swimming underwater with breathing apparatus such as scuba gear — targeting the tank-and-regulator diver who can stay down at depth, not the surface snorkeller or casual bather covered by other water-safety signs. It should be used where the cited standard, facility risk assessment, SDS, emergency plan, or written safety procedure requires this hazard or safety message to be communicated.
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Reference artwork: Wikimedia Commons · License: Public domain
Technical Data
| Legal Standard | ISO 7010:2019 / ISO 3864-1 |
|---|---|
| Color Codes | #FF0000 / Closest practical match: RAL 3020 Traffic Red |
| Viewing Distance | 50 mm: close equipment or package label; 100 mm: approximately 5 m; 200 mm: approximately 10 m; 300 mm: approximately 15 m; 400 mm: approximately 20 m. |
| Review Status | approved / last reviewed 2026-07-07 |
| Jurisdiction Scope | Global, United States, European Union |
| Keywords | p051, iso 7010, prohibition, sub, aqua, diving, prohibit, use, equipment |
Standard Dimensions Table
| Sign Size | Recommended Visibility |
|---|---|
50 mm | close equipment or package label |
100 mm | approximately 5 m |
200 mm | approximately 10 m |
300 mm | approximately 15 m |
400 mm | approximately 20 m. |
Where This Sign Is Used
Port authorities install it at shore entry points, slipways, and quaysides to keep divers out of shipping lanes, ferry routes, and marina fairways where propeller strike is a severe risk, while dams, weirs, and pumping stations ban diving because intake flows can pin a diver against a screen. It also marks the boundaries of protected wreck and archaeological sites, aquaculture farms, and security zones around bridges, terminals, and naval facilities, often posted beside P050 where snorkelling must stop too.
In-Depth Guidance
What ISO 7010 P051 Means
P051 prohibits sub-aqua diving — swimming underwater using breathing apparatus such as scuba gear. The ISO register frames it as an equipment ban — the use of sub-aqua equipment — so the target is the tank-and-regulator diver who can stay down at depth, not the surface snorkeller or casual bather. The pictogram depicts a finned diver wearing a cylinder, crossed by the diagonal red bar.
"Sub-aqua" is the British term for recreational scuba, which reflects the sign's origin in the ISO 20712-1 water safety series developed with beach and inland-water authorities. In practice the sign reads internationally as "no scuba diving", and it is normally installed at shore entry points, slipways, and quaysides where divers would otherwise kit up.
Where and Why Scuba Is Prohibited
Traffic and infrastructure account for most P051 installations. Divers surfacing in a shipping lane, ferry route, or marina fairway are at severe risk of propeller strike, so port authorities exclude them from operational waters. Dams, weirs, and pumping stations ban diving because intakes and outlets create differential-pressure flows capable of pinning a diver against a screen — a hazard that has killed experienced commercial divers, let alone recreational ones.
The other cluster of bans protects what lies underwater. Designated wreck sites and underwater archaeological areas restrict diving to permit holders; aquaculture farms exclude divers from nets and moorings; and security zones around bridges, terminals, and naval facilities prohibit sub-aqua activity entirely. In each case P051 marks the shore or waterline boundary of the restriction.
Not the Same as No Diving (P052)
The naming collision between P051 and P052 causes real specification errors. P052, "no diving", bans headfirst entry into the water — a shallow-pool safety sign. P051 bans underwater swimming with breathing apparatus. Posting P052 at a harbour to keep scuba divers out communicates nothing useful, and posting P051 at a shallow pool is equally wrong. The pictograms resolve the ambiguity: P051's figure is horizontal underwater with a tank, P052's is plunging downward toward a water surface.
P051 also sits one step beyond P050 in the equipment ladder. Where both surface snorkelling and tank diving must stop — typical for busy navigation channels — sites post the two signs together, since banning scuba alone would leave snorkellers legally in the water and just as exposed to vessel traffic.
Frequently Asked Questions
What does sub-aqua diving mean on a safety sign?
Sub-aqua diving is underwater swimming using breathing apparatus — what most people call scuba diving. ISO 7010 defines P051 as prohibiting the use of sub-aqua equipment, so the sign bans tank diving in the marked waters. It does not address headfirst entry from the poolside, which is the separate sign P052.
Why would scuba diving be banned near a dam or pumping station?
Because submerged intakes and outlets move enormous volumes of water and create suction and differential-pressure zones that can hold a diver against a grate with force no human can overcome. These flows are often invisible at the surface and can start without warning when pumps cycle on. Water utilities therefore prohibit all diving around their structures and mark the exclusion with P051.
Can a site ban snorkelling but allow scuba, or the reverse?
Yes, and both happen. Marine parks sometimes permit surface snorkelling over a reef while banning scuba to limit disturbance at depth, which means P051 alone. Conversely, an organized dive site might ban casual snorkelling near boat platforms while running scheduled scuba operations, using P050 alone. The two signs are independent, which is exactly why ISO registers them separately.
Where should P051 signs be installed?
At the points where a diver would enter or prepare to enter: slipways, steps, ladders, beaches, pontoons, and car-park access paths to the shoreline. Since divers plan entries in advance, harbour authorities also publish the restriction in local notices and charts; the physical sign then confirms the boundary on the ground and supports enforcement.