What to do in case of an Ozone leak: emergency procedures and automatic safety systems

An ozone leak should never be treated as a minor operational incident.

Ozone is a powerful oxidising gas and, although extremely useful for industrial water treatment, wastewater treatment, aquaculture, food processing and many other applications, uncontrolled exposure can present a health risk to operators.

A properly engineered ozone installation should therefore not rely solely on an operator noticing a smell or manually pressing an emergency stop.

Ideally, the system should be designed so that an abnormal ozone concentration automatically triggers appropriate actions such as alarm activation, ozone generator shutdown, isolation of the ozone supply and emergency ventilation.

At OXYTRADING UK, operator safety is considered part of the ozone process design itself. We design and integrate complete ozone systems including generation, oxygen supply, injection, monitoring, off-gas destruction and safety controls.

Learn more about our approach to operator safety:

Designing ozone systems for operator safety

Why must an ozone leak be taken seriously?

Ozone – O3 – is one of the most powerful oxidising agents commonly used for industrial treatment processes.

This high reactivity makes ozone highly effective for:

water disinfection;
wastewater oxidation;
odour control;
process water treatment;
aquaculture;
food and beverage applications;
advanced oxidation processes;
industrial air treatment.

However, ozone can also irritate the respiratory system and must therefore be controlled in occupied workplaces.

In Great Britain, the Health and Safety Executive currently specifies a Workplace Exposure Limit for ozone of 0.2 ppm averaged over a 15-minute reference period.

Under the Control of Substances Hazardous to Health Regulations, or COSHH, employers must carry out a suitable and sufficient assessment where employees may be exposed to ozone.

The objective should therefore be to prevent exposure wherever reasonably practicable and to control any remaining risk using appropriate engineering measures.

Where can an ozone leak come from?

An ozone leak does not necessarily originate from the ozone generator itself.

An industrial ozone installation normally contains several components where ozone gas is generated, transported, injected, contacted with water or destroyed.

Potential leak sources include:

damaged ozone tubing;
loose fittings;
degraded seals or O-rings;
materials unsuitable for ozone service;
solenoid valve failures;
check valve failures;
gas line connections;
contact tank off-gas;
degassing systems;
failed ozone destruct units;
excessive pressure;
poor maintenance or incorrect reassembly;
insufficient plant-room ventilation.

For this reason, ozone safety must address the complete ozone system, not simply the generator.

What should you do immediately if an ozone leak is detected?

Every site should have its own documented emergency procedure based on the installation and its COSHH risk assessment.

However, several general principles normally apply.

1. Do not enter the affected area unnecessarily

If an ozone alarm is active, personnel should not simply enter the plant room to investigate the source.

The atmosphere should be considered potentially unsafe until the ozone concentration has been assessed.

Human smell should never be used as the primary safety instrument.

2. Stop ozone generation

Ozone production should be stopped as quickly as the safety design requires.

Ideally, this action should occur automatically.

A fixed ambient ozone detector can be connected to the ozone generator control system or PLC so that an excessive ozone concentration triggers:

generator shutdown;
ozone solenoid valve closure;
isolation of the ozone injection line;
an audible and visual alarm;
a signal to the site control system.

3. Activate or maintain appropriate ventilation

Adequate ventilation is a key engineering control for ozone installations.

Plant rooms where ozone is generated should have sufficient ventilation to allow potentially dangerous accumulations of ozone to be rapidly dispersed.

Depending on the plant design, an ozone alarm can automatically switch the ventilation system into an emergency or high-flow mode.

The extracted air must also be discharged safely so that ozone is not simply transferred into another occupied area.

4. Restrict access to the area

Personnel should follow the site’s emergency procedure and access to the affected area should be controlled until the atmosphere has been confirmed as safe.

Where appropriate, a beacon outside the ozone plant room can provide a clear visual indication that an ozone alarm is active.

5. Measure the ozone concentration before re-entry

The absence of an ozone smell is not sufficient evidence that the area is safe.

Atmospheric ozone concentration should be checked using a suitable direct-reading ozone instrument or monitoring system.

Direct-reading ozone instruments are particularly useful for confirming that concentrations have returned to an acceptable level before personnel re-enter the area.

Automatic safety should respond before an operator has to

For industrial ozone systems, the preferred philosophy is simple:

Detect the abnormal condition and automatically move the process towards a safe state.

Depending on the size and complexity of the installation, an ambient ozone detector can be connected to:

the ozone generator;
the PLC;
the ventilation system;
ozone isolation valves;
audible alarms;
warning beacons;
SCADA or building management systems;
remote alarm systems.

A typical sequence may be:

abnormal ozone concentration detected;
warning alarm activated;
ventilation increased;
ozone generator stopped;
ozone valve closed;
event recorded by the control system;
system prevented from restarting until the fault has been investigated.

This is the principle of a fail-safe ozone installation.

Should an ozone system use several alarm levels?

In many industrial applications, using more than one alarm level can provide a better control strategy.

A lower warning threshold may be used to initiate actions such as:

visual warning;
operator notification;
increased ventilation;
SCADA alarm;
investigation before escalation.

A higher-level alarm may trigger:

automatic ozone generator shutdown;
ozone gas isolation;
audible alarm;
restricted access;
emergency ventilation;
site emergency procedures.

However, alarm setpoints should not simply be copied from another installation.

They should be defined as part of the site’s risk assessment and control philosophy, taking account of the HSE Workplace Exposure Limit, process configuration, detector accuracy, ventilation strategy and expected operating conditions.

UK ozone exposure limits and COSHH

UK operators should pay particular attention to the COSHH framework.

HSE currently gives a Workplace Exposure Limit for ozone of:

0.2 ppm averaged over a 15-minute reference period.

This value is an occupational exposure limit.

It should not automatically be interpreted as the ideal detector alarm setting.

Detector setpoints may need to provide sufficient warning before exposure approaches the regulatory limit.

The appropriate values should therefore be determined through the site’s risk assessment and engineering design.

Under COSHH, employers should first seek to prevent exposure.

Where this cannot reasonably be achieved, exposure must be adequately controlled using appropriate engineering and organisational measures.

Where should an ozone leak detector be installed?

Installing an ozone detector somewhere in the room does not automatically provide effective protection.

Detector location should be selected after reviewing the actual ozone installation and airflow within the space.

Important factors include:

ozone generator location;
ozone pipework;
injection system;
contact tank;
degassing point;
off-gas destruct unit;
ventilation inlet and extraction points;
air movement within the plant room;
operator working locations;
likely leak points;
possible migration routes into adjacent areas.

A detector positioned in a poorly selected location may react too slowly to a leak.

Detector placement should therefore form part of the overall ozone safety assessment.

Why an ozone destruct unit is an important safety component

In water treatment systems, not all ozone injected into the water is necessarily transferred or consumed.

Residual ozone may leave a contact tank as off-gas.

This ozone should not simply be released into an occupied plant room.

An ozone destruct unit converts residual ozone back into oxygen before the gas is safely discharged.

Destruction systems may use catalytic or thermal technology depending on the ozone concentration, gas flow and application.

For critical installations, the destruct system itself can also be monitored.

For example, ozone generation may only be permitted when:

destruct airflow is confirmed;
the ventilation system is operational;
no ambient ozone alarm is active;
the control system confirms normal operating conditions.

If the destruct unit fails, ozone generation can then be stopped automatically.

This type of interlocking forms part of the safety architecture used in professional industrial ozone installations.

Ventilation of an ozone plant room

Ventilation is one of the principal engineering measures available for reducing the risk of ozone accumulation.

The ventilation design should consider:

room volume;
maximum ozone production;
credible leak scenarios;
equipment location;
normal occupancy;
air inlet position;
extraction location;
airflow direction;
where extracted air is discharged.

Where there is a clearly defined source of ozone release, local exhaust ventilation may also be appropriate.

Extracted air may require ozone removal before discharge.

Should the ozone generator be interlocked with the ventilation system?

For many industrial installations this is a sensible engineering approach.

One possible control philosophy is that the ozone generator cannot operate unless the required ventilation is proven to be running.

If airflow is lost:

the generator stops;
ozone injection is isolated;
an alarm is generated.

This prevents ozone production continuing when one of the principal safety controls has failed.

Is a manual emergency stop still required?

Automatic safety systems do not necessarily remove the need for manual emergency controls.

Depending on the installation, an emergency stop can provide an additional means of immediately stopping ozone generation.

Its location is important.

An operator should not have to enter a potentially contaminated ozone room simply to reach the emergency stop.

Can operators investigate an ozone leak themselves?

Only if this is permitted by the site’s safe system of work and the atmosphere has been appropriately assessed.

Investigating an ozone leak may require:

isolation and lockout of the ozone generator;
isolation of the oxygen and ozone supply;
ventilation of the area;
measurement using a portable ozone monitor;
appropriate respiratory protective equipment;
trained and competent personnel.

Respiratory protective equipment may sometimes be necessary when dealing with an ozone leak.

Any RPE used must be suitable for the environment and the user, and personnel must be properly trained.

What should be checked after an ozone alarm?

A falling ozone reading does not mean the incident has been resolved.

Before restarting the system, the cause of the alarm should be identified.

Depending on the installation, checks may include:

ozone tubing;
pipework;
fittings;
seals;
check valves;
solenoid valves;
ozone generator connections;
Venturi injector;
contact tank;
off-gas pipework;
ozone destruct unit;
ventilation system;
ambient ozone detector;
detector calibration;
PLC alarm history;
control system interlocks.

Restarting an ozone installation without identifying the root cause can result in the same incident occurring again.

Eight safety measures to consider for an industrial ozone system

Depending on the application and COSHH risk assessment, an industrial installation may include:

Fixed ambient ozone detection
Warning and high-level alarm thresholds
Automatic ozone generator shutdown
Mechanical ventilation or local exhaust ventilation
Off-gas ozone destruction
An accessible emergency stop
PLC safety interlocks and fault monitoring
A documented emergency procedure and trained operators

Maintenance is part of ozone safety

Safety controls are only useful if they remain effective.

Control measures provided to reduce exposure to hazardous substances must be kept in efficient working order and properly maintained.

For an ozone installation this may include periodic checks of:

ozone detectors;
detector calibration;
ventilation systems;
off-gas destruct units;
ozone-compatible tubing;
seals and fittings;
solenoid valves;
alarms;
emergency stops;
PLC interlocks.

The safety system should therefore be included in the maintenance programme rather than treated as a one-off installation requirement.

An emergency procedure must exist before an ozone leak occurs

The worst time to decide how to respond to an ozone leak is after the alarm has already activated.

A suitable site procedure should define:

who is responsible for stopping the plant;
when evacuation is required;
who may enter the affected area;
how the atmosphere is checked;
what ventilation should operate;
whether RPE is required;
how the leak is investigated;
who authorises restart;
how the event is recorded and reviewed.

Operators should also understand the purpose of the ozone detector, alarm signals and emergency controls.

First aid following significant ozone exposure

Where an individual may have been significantly exposed to ozone, the site’s emergency and first-aid arrangements should be followed.

An affected person should be moved to an uncontaminated atmosphere, kept at rest and medical assistance should be sought when required.

If breathing difficulties are present, trained and competent first-aid personnel should follow the appropriate workplace emergency procedures.

Sites using ozone should incorporate these arrangements into their emergency planning and staff training.

Ozone safety is not just about installing a detector

A detector that only sounds an alarm is useful, but industrial ozone safety can go considerably further.

The real engineering question is not simply:

“Can the installation detect an ozone leak?”

It is:

“What does the installation automatically do when an ozone leak is detected?”

This distinction is important.

A complete ozone safety philosophy considers:

detection;
alarms;
automatic shutdown;
ozone isolation;
ventilation;
off-gas destruction;
safe restart conditions;
operator procedures.

OXYTRADING UK: engineering complete ozone safety systems

OXYTRADING UK specialises in the engineering and integration of professional and industrial ozone solutions.

Our approach is not limited to supplying an ozone generator.

Depending on the project, we can integrate:

ozone generation;
PSA oxygen generation;
ozone injection;
gas/liquid mixing;
contact systems;
ambient ozone monitoring;
dissolved ozone monitoring;
ozone off-gas destruct units;
ventilation interlocks;
PLC control;
automatic shutdown systems;
commissioning;
operator training;
technical and safety assessments.

Our engineering-led approach allows us to work on new systems as well as existing ozone installations requiring optimisation or additional safety measures.

Learn more about our industrial ozone engineering solutions:

Industrial ozone water treatment solutions | Ozone engineering & integration experts UK

You can also discover our ozone water treatment rental solutions:

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FAQ – Ozone leaks and ozone generator safety

What should I do if an ozone alarm activates?

Follow the site’s emergency procedure, avoid unnecessary entry into the affected area, stop ozone generation, ensure appropriate ventilation and verify the ozone concentration before allowing normal access.

On a properly integrated installation, several of these actions can be triggered automatically.

What is the UK workplace exposure limit for ozone?

HSE currently specifies a Workplace Exposure Limit of 0.2 ppm averaged over a 15-minute reference period.

Employers must also assess and control ozone exposure under COSHH where exposure may occur.

Can an ozone detector automatically shut down an ozone generator?

Yes.

Suitable fixed ozone detectors can provide relay, analogue or digital outputs that can be integrated with a PLC or generator control system.

An ozone alarm can therefore trigger automatic generator shutdown and other safety actions.

Can I rely on the smell of ozone to detect a leak?

No.

Odour should not be used as the primary means of determining whether an atmosphere is safe.

Direct measurement with suitable ozone monitoring equipment should be used.

Does an ozone destruct unit prevent all ozone leaks?

No.

An ozone destruct unit is primarily intended to remove residual ozone from process off-gas.

It does not replace leak-tight pipework, ambient ozone detection, ventilation or automatic shutdown controls.

Does every ozone generator require a fixed ozone detector?

The appropriate controls depend on the installation and its risk assessment.

However, fixed atmospheric monitoring is an important safety measure for many industrial ozone installations, particularly plant rooms and systems producing significant quantities of ozone.

Should an ozone generator stop if the ventilation fails?

For many industrial systems this is an appropriate fail-safe strategy.

The generator can be electrically interlocked with the ventilation system so that ozone cannot be produced unless the required airflow has been confirmed.

Conclusion: the best response to an ozone leak is one that has already been engineered

An ozone leak should trigger a structured response:

detection, alarm, shutdown, ventilation, atmospheric measurement and investigation before restart.

But the most important safety work takes place before the incident occurs.

A professionally designed industrial ozone installation should be capable of detecting abnormal ozone levels and automatically placing the process into an appropriate safe condition.

OXYTRADING UK supports clients with complete ozone engineering solutions from feasibility and system sizing through to equipment integration, monitoring, commissioning and safety management.

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