Industrial Diving Gases: What They Are Used For and How They Support Underwater Operations

When commercial divers inspect a pipeline or repair a submerged structure, their breathing-gas supply must support the entire job. That includes reaching the worksite and returning safely, with gas available for any required decompression and emergencies.

The gas needed for a shallow harbour inspection can differ from the mixture used during deep offshore repairs. Increasing water pressure changes how gases affect the body, while demanding work can increase the amount a diver breathes.

Choosing the right industrial diving gases starts with the planned depth and the work divers will be completing. This article explains how different gas mixtures support those tasks and what contractors need to consider when arranging their supply.

What Are Industrial Diving Gases?

Industrial diving gases are individual gases or blended breathing gas mixtures supplied for professional underwater work. They may reach the diver through a hose connected to equipment on the surface or support the pressurised chambers used during saturation diving.

In diving mixtures, oxygen is blended with nitrogen or helium in proportions suited to the working depth. Helium can replace some or all of the nitrogen for deeper work, helping limit nitrogen narcosis and reduce the effort of breathing under pressure.

The required blend depends on where and how it will be used. A gas intended for breathing at depth may differ from one used during decompression, when pressure is gradually reduced before a diver returns to normal surface conditions.

This makes diving gas a broad category of products rather than one interchangeable supply.

Main Types of Breathing Gases Used in Commercial Diving

The differences between breathing mixtures become clearer when considering the problems each addresses. Compressed breathing air is used for some diving operations, while others require mixtures with a different oxygen content or helium replacing some or all of the nitrogen.

Compressed Breathing Air

Air contains approximately 21% oxygen, with nitrogen making up most of the remainder. Commercial divers may receive it from surface equipment through an umbilical line carrying breathing gas or carry it in cylinders where the diving method permits.

At greater depths, breathing the nitrogen contained in air under increased pressure can cause nitrogen narcosis, impairing a diver’s judgement and coordination. A diver may struggle to make decisions or complete a task that would be straightforward at the surface.

Pressure also makes the gas denser, increasing the effort required to breathe. These limitations help explain why deeper work may require helium-based mixtures.

Oxygen and Nitrox

Nitrox combines oxygen and nitrogen. Oxygen-enriched nitrox contains more oxygen than ordinary air, so the diver breathes a smaller proportion of nitrogen at the same depth.

Under appropriate procedures, this can reduce nitrogen uptake and change decompression requirements. However, adding oxygen also restricts how deep the mixture can be used because oxygen becomes toxic when its partial pressure is too high.

Oxygen-rich mixtures may also be used during decompression to help the body eliminate dissolved nitrogen or helium.

Heliox and Trimix

Heliox combines helium and oxygen. Helium has low density and low narcotic potency, making it useful for deeper work where nitrogen narcosis and the effort of breathing denser gas become concerns.

Trimix combines helium, oxygen and nitrogen in proportions selected for the planned depth and diving requirements.

However, helium still dissolves into body tissues under pressure, and reducing pressure too quickly can cause bubbles to form, leading to decompression illness.

How Operating Conditions Affect Gas Requirements

There are a number of factors that determine which gases should be used and how they should be combined. The working depth of a task specifies which gas mixtures are appropriate, while the time underwater and physical effort influence the quantity required.

Depth and Pressure

As a diver goes deeper, the breathing gas must be supplied at a higher pressure to match the increasing water pressure and allow the diver to breathe.

The contribution from oxygen is called its partial pressure, and even if the oxygen percentage stays unchanged, its partial pressure rises as the diver goes deeper.

This is why industrial gas blends cannot be assessed by oxygen percentage alone. It also means some deep-diving mixtures contain too little oxygen for breathing at the surface and must only be used within their specified depth range.

Duration and Diving Method

In surface-supplied diving, the diver breathes gas delivered through an umbilical hose from the surface. Enough gas must be available to complete the work and return safely, with a separate reserve available if the main supply fails.

Saturation divers stay in pressurised chambers between underwater shifts, so their gas supply must also contain enough breathable atmosphere for their rest periods. The total stock must cover both underwater work and chamber use, with additional supplies for decompression and emergencies.

Workload

Moving heavy equipment or working against a current can make a diver breathe harder. So, for example, a diving gas supply estimate for light inspection work may be insufficient for a more demanding repair of the same length of time.

The surface supply must also deliver gas quickly enough to meet that increased breathing demand. Having enough gas in storage does not, by itself, establish that it can reach the diver at the required rate.

Where Industrial Diving Gases Are Used

Commercial divers use breathing gases to carry out work on underwater structures and equipment, including:

• Offshore operations: Examining and repairing subsea infrastructure associated with energy production
• Underwater construction: Installing or repairing submerged foundations and harbour structures
• Inspection: Checking pipelines, vessel hulls, and other equipment for damage or deterioration
• Maintenance: Cleaning submerged equipment or replacing components underwater

Similar tasks can require different supplies. Inspecting a harbour wall close to shore presents different depth and delivery requirements from examining infrastructure offshore.

Location also affects replenishment. A shore-based team may have easier access to replacement cylinders, whereas a vessel’s next gas delivery may depend on a scheduled port call.

Why Gas Quality and Reliable Supply Matter

Contractors must verify that the delivered gas meets the specified composition and that sufficient quantities are available for the planned work and emergency reserves. A large supply cannot compensate for a mixture that is unsuitable for the intended dive.

Verify Composition and Purity

Checking oxygen content establishes only part of the gas’s suitability. Contaminants can still be present even when the intended mixture proportions are correct.

According to HSE guidance, industrial gas calculations should extend beyond expected consumption to allow for losses and contingencies. The dive plan should also establish a minimum remaining supply below which diving must stop.

Clear container identification and gas-analysis documentation help contractors check a delivery against their order.

IMCA’s guidance on breathing-gas supply covers procedures for receiving and accepting diving gases, including composition standards and identification and certification requirements for cylinders and quads.

Plan Beyond Expected Consumption

A repair may take longer than expected, and gas can be lost through leakage or during handling. Supply calculations need to include allowances for these losses while preserving the quantities required for emergencies.

The offshore diving Approved Code of Practice states: “Allowances should be made for leakage, wastage and contingencies.” It also requires diving to stop if the remaining gas supply falls below an agreed minimum.

Delivery planning must also account for storage and handling. For offshore projects, this includes confirming that gas containers can be accommodated and transferred using the equipment available.

Supporting Underwater Operations With Nippon Sanso

Offshore contractors need specified breathing mixtures available before work begins, with replenishment arranged around vessel movements and project demand.

Nippon Sanso’s professional diving solutions include heliox and nitrox, alongside synthetic breathing air and breathing oxygen. It also offers different heliox blends in DNV-certified quads with scheduled deliveries and support for remote projects.

Contact Nippon Sanso to discuss the mixtures and quantities your project requires, together with delivery arrangements for its location.