Across the UK water sector, many hazardous area pumps remain in service as mixed-standard assemblies built up through replacement, refurbishment, and upgrade. Understanding the risks created by these legacy combinations is increasingly important as operators seek safer, clearer, and more reliable pump solutions.
Introduction
Hazardous area pumps certified for use in explosive atmospheres are widely used across the UK water industry, particularly in wastewater treatment, sludge handling, and other hazardous area applications. While hazardous area compliance is well understood in principle, many pumping assets currently in operation were installed or modified during periods when standards, interpretations, and industry practices were still evolving. As a result, many hazardous area pumps in service today are legacy assemblies: combinations of motors, hydraulics, casings, seals, and bearings that may each be compliant in isolation but have not necessarily been assessed or optimised as a complete pump system. This distinction matters because ignition risk, surface temperature, sealing performance, and bearing behaviour are all influenced by how the assembled unit operates under real duty conditions. This article explores the issues that can arise from such arrangements and explains why modern, integrated hazardous area pump designs represent a step change for the water sector.
For operators, the practical question is not whether an individual component carries an appropriate certificate, but whether the complete pump assembly remains suitable for the hazardous zone, duty profile, fluid characteristics, and maintenance regime in which it is used. That distinction is central to managing legacy hazardous area pumps safely.
How Legacy Hazardous Area Assemblies Came to Exist
In many UK water and wastewater facilities, hazardous area pumps have been adapted incrementally over time. A DSEAR review may have driven a motor replacement, a process change may have required higher throughput, or wear issues may have prompted a hydraulic modification. These changes are often made while retaining the original casing or mechanical arrangement in order to manage cost, availability, and downtime. Over time, that practical approach can leave operators with a pump assembly whose components reflect different design assumptions, certification routes, and operating limits.
The result is a hybrid pump assembly where:
- The motor may be certified to later editions of the IEC 60079 series or more recent ATEX certification requirements...
- The impeller reflects older efficiency or solids-handling design practice
- The casing originates from an earlier design era with different assumptions on surface temperature, materials, or cooling
- Seal and bearing arrangements may not align with the revised operating conditions
While this approach can extend asset life, it also introduces risks that are not always apparent during routine operation.
Common Issues Seen in Legacy hazardous area Pumps
Thermal Behaviour Outside Original Assumptions
One of the most frequently encountered problems is unexpected heat generation. Older hydraulic designs can exhibit higher internal losses, particularly when operating away from best efficiency point or handling variable solids content. When these designs are combined with modern motors capable of higher torque or variable-speed operation, localised temperature rises can occur within the pump casing or seal chamber.
In many cases, these thermal effects were not considered in the original hazardous area assessment, particularly where the casing design predates current surface temperature expectations.
Seal and Bearing Limitations
Legacy pump casings often lack the internal geometry or cooling paths required for modern hazardous area rated seals. Elevated seal face temperatures, accelerated bearing wear, and leakage are common consequences, especially in sludge and abrasive wastewater duties. These failures are not always immediate, but they increase maintenance frequency and intervention in hazardous areas.
Component-Level Rather Than Assembly-Level Compliance
A recurring industry challenge is that hazardous area compliance is often considered at component level rather than at complete equipment level. Certified motors and suitably selected components may individually meet their certification requirements, but modifications that affect thermal behaviour, mechanical integrity, or operating parameters should still be assessed to confirm that the assembled equipment remains suitable for its intended hazardous area application. Where multiple parties have modified the asset over an extended service life, the basis for continued conformity can become unclear during audits, refurbishments, or incident investigations.
Maintenance as a Risk Factor
Legacy hazardous area pumps typically require more frequent maintenance. Each intervention within a hazardous area creates the potential for human error, incorrect reassembly, deterioration of explosion protection measures, or the introduction of ignition sources. This risk is especially significant where tolerances, materials, or assembly practices differ between sub-components. In some situations, the frequency of maintenance becomes a greater operational risk than the original duty itself.
The Modern Approach: Hazardous Area Pumps as Integrated Systems
In contrast, newer hazardous area pump designs increasingly adopt a system-level engineering philosophy. Rather than relying on individual component certificates, modern designs assess hazardous area compliance across the complete pump assembly and its intended operating envelope.
Key characteristics of this approach include:
- Hydraulics optimised to minimise internal losses and heat generation
- Integrated thermal analysis covering motor, bearings, seals, and casing
- Clearly defined operating limits aligned with real wastewater and sludge duties
- Hazardous area conformity demonstrated at assembled pump level
- Improved sealing and bearing arrangements designed for continuous hazardous-area operation
This reduces ambiguity and ensures that compliance is maintained under both normal and foreseeable abnormal conditions.
A Typical Water Industry Experience
The following example reflects issues commonly encountered within the sector.
A sludge transfer pump installed in the early 2000s provides a representative example. Following a DSEAR review, the original motor was replaced with an ATEX-rated unit. Several years later, the impeller was modified to increase throughput, while the original casing and seal arrangement remained unchanged. Although the motor remained compliant, repeated seal failures and elevated casing temperatures were observed during high-solids operation. Investigation showed that the revised hydraulic performance had increased internal recirculation and heat generation beyond the original casing design assumptions. Replacing the unit with a modern, integrated hazardous area pump resolved the thermal and sealing issues, reduced maintenance intervention, and simplified compliance documentation.
Practical Lessons for the Industry
For pump specifiers, operators, and asset owners, several key lessons emerge:
Hazardous area compliance should be evaluated at pump assembly level, not assumed from individual certificates
Incremental upgrades can unintentionally increase ignition risk
Early engagement with OEMs helps align hydraulics, mechanical design, and certification
Lifecycle cost and operational risk should be considered alongside capital expenditure
Conclusion
Many hazardous area pumps currently operating in the UK water industry reflect historical design practices and mixed standards. While functional, these legacy assemblies can present hidden thermal, mechanical, and compliance risks. Modern, fully integrated hazardous area pump designs offer a more robust solution, delivering improved reliability, clearer conformity, and reduced maintenance exposure. As organisations continue to strengthen DSEAR compliance and asset integrity programmes and hazardous area awareness continues to grow, system-level hazardous area design is increasingly becoming the industry benchmark.
Closing Statement
The identification of legacy design features or mixed-component assemblies does not necessarily indicate unacceptable risk. In many cases, a robust risk assessment carried out by suitably qualified experienced personnel can demonstrate that the equipment remains suitable for continued service and is unlikely to act as an ignition source, provided appropriate controls, operating limits, and maintenance arrangements are in place.
Source: C&P Engineering