Delta P Underwater Welding — Why This Job is Dangerous!

We all know underwater welding is not easy, and it is undoubtedly one of the dangerous careers out there. When it comes to underwater welding, there are numerous risks and dangers. The most common term you would come across while talking about the dangers of underwater welding is Delta P.

So you might be wondering what the dangers associated with it or how to survive this. Do not worry because we will discuss everything you need to know about Delta P underwater welding today.

What is Delta P in Underwater Welding?

The term Delta P is also said as DP by commercial divers and underwater welders. This refers to a possible diving danger and is a shorthand for ‘Differential Pressure.’ Differential pressure, or DP, is the most noteworthy underwater peril.

The problem is that a hazardous scenario might be difficult to spot immediately. Water from one location tries to pour into another in DP. The pressure differential may build up to hundreds of pounds, luring divers in and making it difficult to get out.

Its may happen in a variety of conditions, such as when water levels in adjacent regions fluctuate and are seeking to equalize or when water is pulled through or towards intakes, pumps, impellers, or thrusters. It can also happen when water is near a gaseous vacuum that is at a lower pressure than the water.

This is the pressure difference between the inside and outside of a vessel. Welders need to be aware of the effects of pressure sickness, which can occur when the pressure difference becomes too great. Symptoms can include headache, dizziness, nausea, vomiting and even death.

Is DP always positive?

By the rule of thumb, pressure can never be negative, and as delta P is also pressure, it can never be negative.

It is always positive; you cannot employ pressure or impart negative energy, and in the case of pressure-volume work, the external pressure is usually constant, while the interior pressure varies.

What are the dangers associated with underwater welding and diving?

It is a hazard, and there are many dangers related to it. Down below, we will see some of the dangers. Divers face unique and severe dangers due to differential pressure.

There is no danger when there is no water flow, but once the flow begins, the forces exerted are generally rather significant.

The dangers can occur in many situations, like when water levels fluctuate on both sides of a boundary, and a submerged or partially submerged hollow structure holds gas at a more tremendous or lower pressure than the surrounding water.

It can also happen when water is mechanically pulled into intakes, such as cooling or fire water intakes in onshore and offshore structures or sea chests on ships. Moreover, it also happen when water is mechanically pushed towards propellers, or other forms of thrusters, on ships.

There are many recorded cases of people dying from this hazards:

  • Often while cleaning dams, drains, or things like that, divers, underwater welders can get sucked into the dams and eventually die due to tremendous water pressure. The same thing happened in January 1989
  • While repairing a pool drain, you can get sucked into the pool seal. This can cause you to get stuck, and you can even die due to lack of air. A similar incident took place in May 1993
  • Another common hazard occurs while cleaning the water tower. The area becomes less visible, and divers often get stuck onto the sudden opening of the drain and die for lack of oxygen, which took place in July 1989.
How strong is underwater pressure?

How do you survive high risk underwater pressure situations?

This is the very risky and can be life-threatening. However, by maintaining certain safety measures, it is possible to survive.

To survive, you must allow pressures to equalize, with only low-pressure diver assistance required. Also, ensure that relevant valves have double redundancy and that divers do not intrude on a DPDZ.

• Know the risks

Spot potential differential pressure concerns with the help of the right experts. Everyone on the job should be prepared for a underwater pressure situation by ensuring that divers have enough assistance in the case of an emergency.

It may pose issues in a variety of situations, and employees should be aware of what to do in the worst-case scenario if a diver is stranded between two pressure levels.

According to the source, this can also assist clients in having a realistic expectation of what the job entails. Assess the dangers posed by any potential differential pressure concerns. (Read more about how deep underwater welders go in this article here.)

• Redirect pressure

Install a device between the two bodies of water where the draw is occurring to alleviate pressure differentials. This might be a screen or a pipe with many openings to prevent divers from being dragged in without their will. Lockout protocols must also be followed correctly.

• Maintain contact with the diver

It is crucial that all the support workers working with the diver should know their location. Moreover, they should be able to communicate with them easily throughout the task.

Divers should have up-to-date equipment and be prepared to respond as the operation develops. If the divers are qualified and have had adequate training, they may be more suited to DP scenarios and should continue with caution.

How do you calculate pressure differences underwater?

To understand underwater pressure difference more efficiently, you need to know how to calculate it. It is a frequently used word that describes the pressure drop over a pipe component like a valve or filter. The word “delta” derives from the Greek word “delta,” which means “change” in English. In this context, it refers to a shift in pressure.

You just need to subtract the output pressure (P2) from the intake pressure to determine the across a valve (P1).

How do you calculate DP?


It is a very risky hazard that can occur due to a change of pressure underwater. Hence, underwater welding, repair works becomes dangerous.

So, to help yourself survive the risk, you must understand what exactly Delta P is and know all the prevention and safety tips.

Thus today, we wrote this article to help you with every detail you need to know. Make sure to read this article and do your own research very carefully before going for underwater works.