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Avoiding confined space pump installation

Author : Simon Hooton, Technical Product Manager - North Ridge Pumps Ltd

03 September 2020

In a range of industries, confined space entry is often required for the maintenance of critical process equipment, but what is confined space entry, and can it be avoided altogether in pump installation?

Image: Shutterstock
Image: Shutterstock

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Confined space entry is access to an area within industry which satisfy one of the following criteria:

- There is a limited opening for entry and exit

- The space is not designed for continuous human occupancy

- The space is large enough for a person to enter and undertake work

Examples of areas include sewers, above and below ground tanks, reaction vessels, enclosed drains, ductwork, chambers and poorly ventilated rooms which are not always obvious as dangers. There are various risks usually signifying a confined space which are not always apparent to the entrant. These include lack of oxygen, poisonous gas vapour, and dust & fire.

Spaces can lack ventilation or contain gases emitted from previously stored cargo. Products such as grain, slurry, or wood can emit gasses which are not always obvious or visible without sensing equipment. Fluids can also hold dangerous gases, with them being released if disturbed.

Suction lift pump
Suction lift pump

Nitrogen, or CO2 can be elevated at noxious levels in such environments, with some processes absorbing oxygen which can reduce already low oxygen levels. Areas do not need to have liquids present to be dangerous. Zones can still contain elevated levels of poisonous and toxic gas even when empty.

Fires or explosions can occur from vapours and residue within tanks which can sometimes be odourless and easily ignitable due to its concentration. Dust generated from products such as cement, flour, cargo, scrap, and dry bulk handling can be combustible and ignite quickly, or it can contain high concentrations of silica leading to breathing difficulties or future health issues.

Product filling or bridging

In storage tanks filled with grain, sludge or slurry, product can bridge causing a temporary gap prone to sudden collapse or in some situations liquids or solids can quickly fill space with little or no warning from another process. In 2017, workers in East Greenwich were performing preparatory work in a sewer when a 150-year old penstock failed, engulfing the workers in sewage and carrying them along the sewer.

Excess temperature

Areas in industry which are used for cooking, conveying of steam, ventilation or thermal transfer can lead to high temperatures within areas requiring admission. If access is made before temperature levels are safe, it can lead to dangerous increases in body temperature in excess of what can be handled capably.

Image: Shutterstock
Image: Shutterstock

What does entry involve?

Confined space entry involves a number of exhaustive procedures ensuring entry and exit to such areas is undertaken with mitigation to risk. First and foremost a risk assessment is conducted to establish procedures, processes, and method for work to be undertaken.

Equipment required includes a provision of oxygen made in the form of breathing apparatus, communication equipment, rescue harness & hoist to enable easy extraction of personnel, provision of tools, and lighting.

A permit to work ensures a formal check is undertaken, ensuring a safe system of work is in place, that there is communication between management, supervisors and operators with clear indications of who is to undertake a task, who bears responsibility for precautions, testing of equipment, emergency arrangements, monitoring and ensuring work is undertaken as expected.

What are the costs?

Access usually requires a full method statement and a risk assessment with entry usually requires 3 people, the entrant, an attendant, and a supervisor with equipment. Operators are expected to remain fully trained with training costing between £500-£1000 per person each year. Such risks to confined space entry should not be underestimated. There continues to be 15 deaths per year on average and, with the average Health and Safety fine being £150,000 in 2019, steps are being taken to mitigate or avoid such entry.

Self-priming pump
Self-priming pump

Regular training is expected, with qualifications kept up to date. Due to the associated costs of ongoing training, certification, and risks, companies often choose to outsource this type of maintenance since retaining such highly qualified and experienced staff becomes difficult. Such highly experienced and certified workers are usually highly sought after with their marketplace value increasing which means turnover in the role is high.

As maintenance is outsourced and outside the control of the plant, downtime periods can be longer, and expensive when required urgently.

How can confined space be modified so entry is not required?

Avoiding confined space is actively encouraged by the HSE to reduce risks, one of which is to have work performed externally. This can involve having pumps mounted outside of tanks, process vessels or in pits. Typically, many applications involve a submersible pump which is often the cheapest initial solution which are guiderail or foot mounted. This can be replaced through the use of immersion or self-priming pumps.

A self-priming pump is a pump which can be surface mounted, outside of tanks, silos and pits to extract fluids. Depending on the nature of the liquid, abrasiveness and viscosity, pumps can be of non-clog design handling large solids, which are fibrous and contain gas slugs.

Low maintenance designs enable part replacement by a single person without the need of additional equipment. Sludges, slurries or other viscous matter can be handled capably by such units with the added benefit of being easily accessible, ensuring periodic maintenance is straightforward.

Typical pump lifetime ownership costs
Typical pump lifetime ownership costs

Another alternative is an immersion pump which can be installed in the top of the tank with working parts operated via a shaft within tanks. Designs are available which can be up to 100M long working with fluids from water to sludges and slurries. As the motor is mounted externally to the tank and not immersed, it is less susceptible to corrosion, as well as being easily accessible for the early detection of issues.

The costed case

So, how much of ownership does the initial outlay of a pump account for? Typically, a pump’s initial purchase price only accounts for 10% of the initial investment. Around 45% of a pump’s costs are energy use, with 30% of its cost being operation, maintenance and repair, 5% downtime and 10% installation and disposal.

However, with confined space entry ongoing maintenance costs can be as much as 15 times the cost of a total pumps cost, meaning designers should seek to engineer out pumps installed in such manner.

Maintenance benefits

Simon Hooton, North Ridge Pumps Ltd
Simon Hooton, North Ridge Pumps Ltd

Installing pumps externally to tanks provides four main benefits to plant owners and operators which include:

1. Maintenance can be performed by as little as one or two people, at short notice, with little additional equipment and without entry to confined space.

2. Longer motor life & quicker sourcing – As motors are externally mounted, outside of the pumped fluid they are less susceptible to corrosion. Surface mounted pumps typically use standard motor frame sizes enabling easy local sourcing whereas submersible pumps use bespoke motors typically only available from the original manufacturer which are less likely to be available during an emergency.

3. When a flammable liquid is being pumped, manufacturers are no longer supplying submersible pumps for flammable fluid transfer, often meaning surface mounted pumps are the only option.

4. Early detection of issues as symptoms can be easily noticeable on surface mounted pumps. Issues such as grinding, high pitch squealing, or vibration are easily noticeable on surface mounted pumps. Submerged pumps are usually out of sight and out of mind with failure only apparent when the unit fails, after which it is then replaced.

Whatever your process involves, it is imperative a holistic approach is undertaken, with full cost of ownership and maintenance included within the process. Providing any project is engineered towards lowest lifecycle costs and not solely initial outlay, it is likely many confined space installations can be eliminated.

About the author:

Simon Hooton is a Technical Product Manager at North Ridge Pumps Ltd. He has operated in the pump industry for over 10 years since completing his business degree. Simon is a specialist in a wide range of pump types from centrifugal to positive displacement and has been involved in a variety of projects from the handling of seawater, to oils, resins and sludges.

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