Wastewater DSEAR Verification: London Case Study
A commissioning-stage DSEAR verification and risk assessment for wastewater worksites forming part of a major London infrastructure project.
Sector
Wastewater Infrastructure
Client
Confidential Contractors
Location
London
Project Stage
Commissioning and Handover
Project Scope
DSEAR Verification and Risk Assessment
Project Overview
DW Consulting Services was appointed to complete a DSEAR verification of overall explosion safety for multiple waste water handling worksites spanning across a major infrastructure project in London.
The worksites contained interception and valve chambers, drop shafts, gas analysers, air inlets, hydraulic power units, and uninterruptible power supplies (UPS).
The work was undertaken during commissioning to validate that an appropriate basis of safety had been selected, and that the worksites had been designed and constructed in compliance with the requirements of DSEAR.
Client Challenge
The worksites could receive a variety of effluent, including petrol. The potential for sewer gas generation and hydrogen generation from the UPS batteries was also present. Petrol vapour, flammable sewer gases and hydrogen are treated as dangerous substances under DSEAR.
The client required the worksites to be verified in line with Regulation 7(4) of DSEAR before being used for the first time to ensure that all credible hazards had been identified, that appropriate control measures had been implemented, and that the workplaces complied with the requirements of DSEAR.
Scope of DSEAR Verification
The verification considered whether the fire and explosion hazards had been identified, and that the control and mitigation measures selected and identified during the design and hazard-study process had been correctly selected, installed and documented. The review covered the DSEAR risk assessment, hazardous area classification, basis of safety, ATEX equipment selection and inspection, ventilation, emergency arrangements, competency records, and outstanding actions.
Why was DSEAR Verification Required?
Regulation 7(4) of DSEAR requires the overall explosion safety of a workplace containing zoned areas to be verified by a competent person before the workplace is brought into use for the first time. The verification therefore formed an important commissioning and handover deliverable.
Technical Approach
Information Gathering
A comprehensive list of required information was sent to the client for review, along with a structure for this to be supplied in. A site visit was also conducted to review the worksites and gather additional information. This included:
Dangerous substances details (e.g. SDSs and quantity of substance inventory)
Design intent and basis of safety
Risk assessments (e.g. DSEAR risk assessments, HAZID and HAZOP reports, ignition hazard assessments)
Action trackers
Initial ATEX equipment inspection records and asset register
Proof of personnel competency (e.g. CompEx certificates)
Emergency response plans
Ventilation commissioning reports
Leak testing records
Photographs of the worksites
This information was provided in a clear, structured manner which allowed for efficient review and identification of any obvious gaps.
Document and Basis of Safety Review
The first step in verifying the overall explosion safety of the worksites was to establish a basis of safety for each unit operation where dangerous substances were liable to be present.
It was discovered that, although a hazardous area classification (HAC) had been conducted, a DSEAR risk assessment had not been performed for the worksites. DW Consulting Services conducted a risk assessment in line with Regulation 5 of DSEAR for the worksites, which identified credible fire and explosion hazards and established a suitable basis of safety for each unit operation - this was in addition to the DSEAR Verification works, but was required in order for the site to achieve compliance and validate that the risks had been properly controlled and reduced to ALARP.
For the sewage handling and ventilation areas of the site, the basis of safety was determined to be Control of Ignition Sources. For the UPS battery installations, the basis of safety was determined to be a combination of Prevention of the Formation of an Explosive Atmosphere and Control of Ignition Sources.
The available documentation was then reviewed to determine whether the basis of safety had been sufficiently implemented, and if there were any outstanding actions from hazard studies performed which were still to be completed.
Examples of documentation reviewed to support the Control of Ignition sources basis of safety included:
Hazardous Area Classification (HAC) Drawings - drawings had been produced which showed the classified zones in both plan and elevation
ATEX Asset Register and Initial Inspection - the client was able to demonstrate that suitable equipment had been selected and installed by competent personnel by producing the initial ATEX inspection records performed in line with BS EN 60079-14 and BS EN 60079-17, as-built electrical drawings, ATEX certificates for all components, and CompEx certification records
Competency Records - valid CompEx certification for relevant modules (EX01 - EX04) for personnel who had performed the electrical equipment installation was provided, as well as for the designers (modules 12A and 12B)
The results of this review were tabulated in a report, with each criterion either marked as complete, partially complete or not complete, along with commentary supporting this stance and pragmatic actions for what was required to fill the gaps and achieve compliance.
The main gaps which were identified were that no suitable DSEAR risk assessment had been conducted, the Emergency Response Plans (ERPs) did not meet all the requirements of Regulation 9 of DSEAR, and some minor discrepancies were identified between the hazardous area classification and HAC drawings.
Overall, the worksites were deemed to be safe to operate in compliance with DSEAR, with only minor remedial actions required.
Next Steps and Action Close Out
Following issue of the DSEAR Verification reports, an action tracker was created to facilitate close-out of the recommendations in the report. DW Consulting Services reviewed additional supporting evidence provided after the actions had been completed, and confirmed whether the evidence was sufficient to close each action.
Key Findings
DSEAR Risk Assessment Gap
Although a hazardous area classification had been completed, no suitable DSEAR risk assessment had been completed for the worksites.
Emergency Arrangements
The emergency-response plans required additional information to fully address the relevant DSEAR requirements.
Hazardous Area Documentation
Minor discrepancies were identified between the hazardous area classification assessment and the issued HAC drawings.
Overall Verification Status
The installations were considered suitable to enter operation, subject to completion and formal close-out of the identified minor remedial actions.
Project Outcome
The verification established that the main fire and explosion safety measures had been appropriately incorporated into the design and construction of the worksites. A limited number of remedial actions were identified and recorded in a structured action tracker.
DW Consulting Services subsequently reviewed the close-out evidence and confirmed where the actions had been satisfactorily completed. The final verification documentation was included in the project handover pack, providing the end user with a clear record of the DSEAR assessment, verification status, and remaining operational responsibilities.
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