Guide
Work safely in confined spaces on drainage projects
How to comply with the Confined Spaces Regulations 1997 when working in manholes, sewers, chambers, and service ducts on drainage projects. Covers risk assessment, safe systems of work, atmospheric monitoring, emergency rescue arrangements, and permits to enter.
If your construction work involves entering manholes, sewers, inspection chambers, pumping stations, valve chambers, or service ducts, you must comply with the Confined Spaces Regulations 1997 (CSR 1997). These regulations impose strict duties because confined space entry is one of the most dangerous activities in the construction industry.
Drainage confined spaces present specific hazards that can kill without warning. Toxic gases such as hydrogen sulphide build up from decomposing organic matter in sewers. Oxygen levels can drop below safe limits in enclosed chambers. Water levels can rise suddenly from upstream discharge or storm events. Every year, workers are killed or seriously injured in drainage confined spaces — often because basic precautions were not followed.
Non-compliance is a criminal offence carrying an unlimited fine and up to 2 years’ imprisonment on indictment. Work in confined spaces also falls within CDM 2015 Schedule 3 particular risks, meaning your construction phase plan must specifically address these hazards.
This guide sets out the steps you must take before, during, and after confined space entry on drainage projects.
1. Determine whether entry can be avoided
Your first legal duty under Regulation 4(1) is to avoid entering a confined space unless entry is not reasonably practicable. Before planning any entry, consider whether the work can be done without anyone going inside.
Alternatives to entry include:
- CCTV surveys — remote inspection of sewer and pipe condition
- Mechanical cleaning — high-pressure jetting to clear blockages without manual access
- Automated monitoring — remote sensors for water level, flow, or gas detection
- Redesigning the work method — carrying out repairs or modifications from outside
If any alternative is reasonably practicable, you must use it. Document your assessment of alternatives and the reasons entry is necessary before proceeding.
2. Carry out a confined space risk assessment
Where entry cannot be avoided, you must carry out a suitable and sufficient risk assessment specific to the confined space and the work to be done. A generic risk assessment is not adequate — each confined space has different characteristics and hazards.
Your risk assessment must identify:
- The type and dimensions of the confined space (manhole, sewer, chamber, duct)
- The hazards present or likely to arise (gases, oxygen depletion, drowning, engulfment, temperature)
- The work to be carried out and its duration
- The number of people who will enter
- The equipment needed for safe entry, work, and rescue
- Previous incidents or known risks at the location
- Weather conditions and upstream activities that could affect the space
The risk assessment must be carried out by a competent person with knowledge of the specific hazards in drainage confined spaces. Review and update the assessment whenever conditions change.
3. Establish a safe system of work
Regulation 4(2) requires you to establish a safe system of work that renders work in the confined space without risk to health, so far as is reasonably practicable. Your safe system must cover every stage from preparation through to exit.
Your safe system of work must include:
- Appointment of a competent supervisor who controls and oversees the entry
- Isolation of services — lock off pumps, valves, and upstream flows to prevent flooding or release of harmful substances
- Ventilation — forced ventilation to maintain breathable atmosphere throughout the work
- Atmospheric testing — continuous monitoring for oxygen, hydrogen sulphide, methane, carbon monoxide, and carbon dioxide using a calibrated multi-gas detector
- Communication procedures — maintaining constant contact between the entrant and the attendant outside
- Limited working time — setting maximum entry duration based on conditions and physical demands
- PPE and RPE — appropriate personal and respiratory protective equipment for identified hazards
Pre-entry atmospheric testing is critical. Test the atmosphere before anyone enters using a remote sampling probe lowered into the space. Do not rely on sense of smell — hydrogen sulphide deadens the olfactory nerve above 100 ppm, so you may not detect lethal concentrations.
4. Set up emergency rescue arrangements
Regulation 5 requires that suitable and sufficient rescue arrangements must be in place BEFORE any person enters a confined space. This is not optional and cannot be deferred until an emergency occurs.
Your emergency arrangements must provide:
- Trained rescue team — at least one person trained in confined space rescue must remain outside the space at all times during entry
- Rescue equipment — rescue harness and lifeline, mechanical lifting device (tripod and winch), self-contained breathing apparatus, and resuscitation equipment
- Communication equipment — reliable means of raising the alarm and calling for additional assistance
- Fire and rescue service liaison — inform the local fire and rescue service in advance where high-risk entries are planned
- First aid provision — trained first aider and equipment on site
- Hospital proximity — identify the nearest hospital with an accident and emergency department and plan the route
The attendant (top person) must never enter the space to attempt rescue. Untrained rescue attempts are one of the most common causes of multiple fatalities in confined spaces. The attendant’s role is to monitor the entrant’s welfare, maintain communication, and raise the alarm if something goes wrong.
5. Implement the permit to enter system
A permit to enter is a formal documented control that authorises entry into a specific confined space for a specific task within a defined time period. HSE’s Approved Code of Practice L101 requires a permit system for all but the most straightforward confined space entries.
The permit must specify:
- The confined space to be entered (location and identification)
- The work to be carried out
- The hazards identified in the risk assessment
- The precautions required (isolation, ventilation, monitoring, PPE)
- Time limits for the entry
- The names of authorised personnel (supervisor, entrants, attendant, rescue team)
- Emergency procedures and rescue arrangements
The permit must be issued by a competent person who has assessed the risks and verified that all precautions are in place. It is time-limited and must be cancelled and re-issued if conditions change — for example, if the weather changes, different work is needed, or there is a shift change.
6. Know when to report and what happens next
If something goes wrong during confined space work, you have legal reporting obligations under RIDDOR 2013. Loss of consciousness due to gas or asphyxiation in a confined space is a reportable dangerous occurrence — even if the person recovers fully.
Common mistakes to avoid
Skipping the avoidance assessment: Going straight to planning an entry without first considering whether alternatives exist. This is a breach of Regulation 4(1) and HSE inspectors will ask for evidence of your assessment.
Using generic risk assessments: A single risk assessment for “confined space entry” does not meet the legal standard. Each entry must be assessed individually, accounting for the specific space, conditions, and work.
Relying on sense of smell for gas detection: Hydrogen sulphide deadens the sense of smell at higher concentrations. By the time you cannot smell it, the concentration may already be lethal. Always use calibrated instruments.
No dedicated rescue team: Planning to “call 999” is not a rescue arrangement. Rescue equipment and a trained person must be on site and ready before entry begins.
Attendant entering the space: If the entrant becomes unresponsive, the natural reaction is to go in after them. This is exactly how confined space fatalities become multiple fatalities. Train your attendant to use the rescue equipment from outside.
-
Assess whether entry can be avoided
Before any confined space work, carry out a formal assessment of alternatives to entry (CCTV, jetting, remote monitoring). Document the assessment and the reasons entry is necessary. Keep this record with the risk assessment.
-
Carry out a site-specific risk assessment
Assess each confined space individually. Identify the specific hazards (gases, oxygen levels, water ingress, engulfment), the work to be done, and the controls required. Review the assessment if conditions change.
-
Prepare the safe system of work
Document the safe system covering supervision, service isolation, ventilation, atmospheric monitoring, communication, working time limits, and PPE. Brief everyone involved before entry begins.
-
Set up rescue arrangements before entry
Position rescue equipment (tripod, winch, harness, lifeline, breathing apparatus, resuscitation equipment) at the entry point. Ensure at least one trained rescuer remains outside throughout. Notify the local fire service for high-risk entries.
-
Issue the permit to enter
A competent person must issue a time-limited permit specifying the space, work, hazards, precautions, personnel, and emergency procedures. Cancel and re-issue if conditions change.
-
Test the atmosphere before and during entry
Use a calibrated multi-gas detector with a remote sampling probe to test the atmosphere before entry. Continue monitoring continuously throughout the work. Evacuate immediately if any reading exceeds safe limits.
-
Report any incident under RIDDOR
Report any loss of consciousness, serious injury, or dangerous occurrence to HSE immediately by telephone for deaths and major injuries, or online within 10 days for other reportable incidents. Retain records for 3 years.