Confined spaces can look harmless from the outside, but the atmosphere inside may be oxygen-deficient, oxygen-enriched, flammable, toxic or unstable.

That is why atmospheric testing is one of the most important steps before and during confined-space work.

For Canadian industrial plants, utilities, municipalities, oil and gas sites, mines, water and wastewater facilities, food-processing plants, construction projects and maintenance teams, confined-space measurement should never be treated as a quick “take one reading and enter” task.

A safe confined-space testing process should answer:

• Is there enough oxygen?
• Is the atmosphere oxygen-enriched?
• Are flammable gases, vapours or combustible dusts present?
• Are toxic gases present?
• Could conditions change after entry?
• Is ventilation required?
• Is continuous monitoring required?
• Is the gas detector properly calibrated and bump-tested?
• Is the entrant wearing a personal monitor where required?
• Is there an attendant and rescue plan?
• Is any electrical, mechanical, hydraulic, pneumatic, chemical or thermal energy controlled?

CCOHS notes that when a worker must enter a confined space or when there is a potential atmospheric hazard, a competent person must perform pre-entry atmospheric testing to verify oxygen and identify toxic, flammable or explosive substances that may be present, using appropriate calibrated instruments according to manufacturer directions.

What Is a Confined Space?

A confined space is not simply a small room.

A confined space is generally an enclosed or partially enclosed area that is not designed for continuous human occupancy and may have restricted entry or exit. It may also contain hazardous conditions such as poor air movement, dangerous gases, oxygen deficiency, mechanical hazards, engulfment hazards or uncontrolled energy.

Common examples include:

• Tanks
• Vessels
• Silos
• Vaults
• Pits
• Manholes
• Sewers
• Tunnels
• Boilers
• Ducts
• Crawl spaces
• Lift stations
• Pump chambers
• Trenches
• Process vessels
• Storage bins
• Utility chambers
• Underground electrical vaults

The exact legal definition and requirements vary by Canadian jurisdiction, so the employer must follow the applicable federal, provincial, territorial and site-specific requirements.

Why Confined-Space Atmospheres Are Dangerous

The most dangerous confined-space hazards are often invisible.

A worker may not see, smell or feel a problem until it is too late.

Atmospheric hazards can include:

• Oxygen deficiency
• Oxygen enrichment
• Flammable gases or vapours
• Combustible dust
• Toxic gases
• Chemical vapours
• Biological gases
• Carbon monoxide
• Hydrogen sulphide
• Carbon dioxide
• Volatile organic compounds
• Solvent vapours
• Nitrogen or inert gas displacement

Government of Canada guidance states that normal air has approximately 21% oxygen, that oxygen deficiency can occur when oxygen is displaced or consumed, and that the minimum concentration deemed safe for entering a confined space is set at 19.5%. It also warns that oxygen-enriched atmospheres above 23% can cause materials such as clothing and hair to burn violently when ignited.

Common Atmospheric Hazards to Measure

Oxygen Deficiency

Oxygen deficiency can occur when oxygen is displaced or consumed.

Common causes include:

• Nitrogen purging
• Carbon dioxide accumulation
• Rusting or oxidation
• Biological decomposition
• Welding or hot work
• Combustion
• Fire aftermath
• Worker respiration in poorly ventilated spaces
• Inert gas introduction
• Displacement by heavier-than-air gases

Oxygen deficiency is especially dangerous because judgment and physical ability can decline quickly. Government of Canada guidance states that at around 16% oxygen, judgment and breathing are impaired, and at around 12% oxygen, a person may lose consciousness and die unless moved to fresh air.

Oxygen Enrichment

Too much oxygen is also dangerous.

Oxygen-enriched atmospheres increase fire and explosion risk because materials ignite more easily and burn more violently.

Never use pure oxygen to ventilate a confined space. CCOHS and Government of Canada both warn that oxygen should not be substituted for fresh air because oxygen enrichment significantly increases fire and explosion hazards.

Flammable Gases and Vapours

Flammable gases and vapours can create an explosion hazard when mixed with air.

Examples include:

• Methane
• Propane
• Gasoline vapours
• Solvent vapours
• Hydrogen
• Fuel vapours
• Process gases
• Sewer gases

Combustible gases have a lower explosive limit and an upper explosive limit. Government of Canada explains that ignition occurs only when the gas-air mixture is within that explosive range, with methane given as an example between 5% and 15% in air.

Toxic Gases

Toxic gases can cause poisoning, unconsciousness, respiratory irritation or death.

Examples include:

• Hydrogen sulphide
• Carbon monoxide
• Chlorine
• Ammonia
• Sulphur dioxide
• Volatile organic compounds
• Solvent vapours
• Process-specific toxic gases

Government of Canada identifies hydrogen sulphide as a toxic gas commonly found in hazardous confined spaces, and notes that toxic gases can create chemical asphyxiation or irritation hazards.

Pre-Entry Testing vs Continuous Monitoring

Pre-Entry Testing

Pre-entry testing is performed before a worker enters the confined space.

It helps determine whether the space is safe to enter under the approved procedure.

Pre-entry testing may include:

• Oxygen level
• Flammable gas or vapour
• Combustible dust
• Toxic gases
• Process-specific contaminants
• Air stratification at multiple levels
• Testing around corners, pockets or low points
• Testing after purging or ventilation

CCOHS summarizes Canadian jurisdictional requirements and notes that pre-entry testing must be performed by a competent or qualified person using appropriate and calibrated instruments, with additional testing as often as necessary after entry.

Continuous Monitoring

Continuous monitoring is used when the atmosphere could change while workers are inside.

This may be required when:

• The work could generate fumes or vapours
• Hot work is performed
• Ventilation may fail
• The space contains residues
• Liquids or sludge remain
• The atmosphere could stratify
• Adjacent processes could introduce hazards
• Toxic gas could enter the space
• Combustible gas could accumulate
• Oxygen levels could change
• The work duration is long
• The confined-space plan requires it

CCOHS notes that where the atmosphere may change unpredictably after a worker enters, continuous monitoring may be required, and in some jurisdictions continuous monitoring is required for hazardous confined spaces.

Why One Reading Is Not Enough

A single gas reading at the opening of the space may not represent the full confined-space atmosphere.

Conditions can vary because of:

• Gas density
• Poor air movement
• Internal compartments
• Sludge or residue
• Pockets behind baffles
• Low points
• High points
• Adjacent lines
• Temperature differences
• Mechanical ventilation pattern
• Worker activity
• Hot work
• Cleaning chemicals
• Disturbed material
• Leaks or backflow

CCOHS specifically warns that air movement should be considered because pockets of toxic gases can remain even when mechanical ventilation is used.

A good testing process checks the space in a way that reflects the actual hazards, not only the easiest point to reach.

Recommended Gas Testing Sequence

A common atmospheric testing sequence is:

1. Oxygen
2. Flammable gases or vapours
3. Toxic gases

This order matters because many combustible gas sensors depend on adequate oxygen to operate correctly. If oxygen is too low, the combustible gas reading may not be reliable.

For Canadian copy, avoid presenting one universal sequence as a replacement for site procedure. Use this safer wording:

Follow the confined-space plan, gas detector manufacturer instructions and applicable Canadian jurisdictional requirements. Where required, test oxygen first, then flammable or explosive substances, then toxic gases.

Gas Detector Types Used in Confined Spaces

Multi-Gas Detector

A standard confined-space gas monitor often measures:

• Oxygen
• LEL combustible gases
• Carbon monoxide
• Hydrogen sulphide

This is commonly called a four-gas monitor.

RKI describes the GX-3R as a four-gas confined-space monitor that simultaneously detects LEL combustibles, oxygen, carbon monoxide and hydrogen sulphide. It is designed to be worn in the worker’s breathing zone and provides audible, visual and vibration alarms.

Pumped Sample-Draw Monitor

A pumped gas monitor is used to sample the atmosphere before entry or from a distance.

This is useful when testing:

• Deep tanks
• Manholes
• Vertical entries
• Underground vaults
• Spaces with limited access
• Areas where workers should not enter before sampling
• Spaces that require remote sampling at multiple depths

The RKI Eagle 2 is a sample-draw monitor with a strong internal pump. RKI states that it can draw samples from up to 125 feet and offers standard confined-space protection for LEL, oxygen, hydrogen sulphide and carbon monoxide, along with optional sensors such as PID for VOCs and infrared sensors for carbon dioxide or methane.

Personal Monitor

A personal monitor is worn by the entrant, typically near the breathing zone.

It helps warn the worker if the atmosphere changes during entry.

The JM Test source article recommends using the RKI Eagle 2 for initial confined-space testing and the RKI GX-2009 or GX-3R as personal monitors to maintain verification of the work environment.

RKI Eagle 2 for Initial Confined-Space Testing

The RKI Eagle 2 is suitable for initial testing where a pumped sample-draw monitor is needed.

It can be useful for:

• Remote sampling
• Vertical spaces
• Tanks
• Vaults
• Manholes
• Pump stations
• Process vessels
• Spaces where the atmosphere must be checked before entry

RKI states that the Eagle 2 offers standard confined-space protection for LEL, O₂, H₂S and CO, and can be configured with additional sensors including PID for VOCs, infrared CO₂, methane, hydrocarbons and other toxic gases.

For Canadian use, the key point is:

Select sensors based on the actual confined-space hazard assessment. A four-gas monitor may not detect every hazard present in the space.

For example, a standard four-gas monitor may not detect carbon dioxide or VOCs unless equipped with the correct sensors.

RKI GX-3R for Personal Monitoring

The RKI GX-3R is a compact personal four-gas monitor.

It can simultaneously monitor:

• LEL combustible gases
• Oxygen
• Carbon monoxide
• Hydrogen sulphide

RKI describes it as a small, lightweight four-gas monitor that can be clipped in a worker’s breathing zone, with audible, visual and vibration alarms and approximately 25 hours of lithium-ion battery operation.

This makes it useful for workers who need continuous awareness of atmospheric conditions while inside or near a confined space.

However, a personal monitor does not replace the confined-space plan, attendant, rescue plan, ventilation controls or pre-entry testing.

Bump Testing and Calibration

A gas detector is only useful if it is working correctly.

Before relying on a detector, confirm:

• Calibration status
• Bump test status
• Sensor configuration
• Battery condition
• Pump function
• Tubing and probe condition
• Filters
• Alarm function
• Sensor response
• Date and time settings
• Data logging where required

A bump test checks whether the detector responds to a known gas challenge.

A calibration adjusts or verifies sensor response against a known gas concentration.

CCOHS says appropriate and calibrated test instruments must be used according to the manufacturer’s directions.

For the Canadian page, use:

Follow the gas detector manufacturer’s calibration and bump-test instructions, the employer’s confined-space programme and the applicable jurisdictional requirements.

Ventilation and Retesting

Ventilation can improve a confined-space atmosphere, but it does not remove the need for testing.

Ventilation should be planned around:

• Space size
• Shape and internal obstructions
• Gas density
• Entry point
• Exhaust path
• Fresh-air source
• Potential ignition sources
• Hot work
• Contaminant source
• Whether air could recirculate
• Whether the exhaust could affect workers outside

CCOHS says that if potential flammable atmosphere hazards are identified during initial testing, the space should be cleaned, purged, ventilated and retested before entry is allowed. Only after testing is within allowable limits should entry occur.

Also important:

Do not use oxygen for ventilation. Use clean fresh air or an approved ventilation method.

Electrical Testing in Confined Spaces

Some confined-space work involves electrical measurement, troubleshooting or maintenance.

Examples include:

• Electrical vaults
• Pump stations
• Motor-control chambers
• Underground utility spaces
• Instrumentation pits
• Lift stations
• Tank farms
• Process vessels with sensors
• Lighting or power circuits
• Temporary power and tools

In these situations, confined-space controls and electrical-safety controls must work together.

Electrical risks may include:

• Shock
• Arc flash
• Stored energy
• Energized conductors
• Poor lighting
• Wet surfaces
• Limited movement
• Difficult rescue
• Conductive surroundings
• Temporary cords
• Battery systems
• Control circuits
• Explosion risk if flammable gas is present

CSA Z462:24 reorganized requirements for establishing an electrically safe work condition and added that absence of voltage must be verified at each point of work. It also provides requirements and guidance for safe work procedures, PPE selection and qualified electrical workers.

For the Canadian article, use this safety framing:

If electrical measurement is required in or near a confined space, follow both the confined-space entry procedure and the site electrical safety programme. De-energize and lock out hazardous energy where practical, verify absence of voltage where required, and use properly rated test instruments and PPE.

Energy Control Before Entry

Atmospheric testing is critical, but it is not the only confined-space safety control.

Hazardous energy must also be controlled.

This may include:

• Electrical energy
• Mechanical energy
• Hydraulic energy
• Pneumatic energy
• Thermal energy
• Chemical energy
• Gravity or stored mechanical energy
• Process flow
• Agitators
• Conveyors
• Pumps
• Valves
• Steam
• Pressurized lines

CCOHS states that potentially hazardous energy sources such as electrical, mechanical, hydraulic, pneumatic, chemical or thermal energy must be de-energized or isolated and locked out before entry so equipment cannot turn on unintentionally. If isolation is not possible, the hazard must be controlled in a way that eliminates or minimizes worker exposure.

Confined-Space Roles

A safe confined-space entry usually involves defined roles.

Entrant

The entrant is the worker entering the confined space.

The entrant should understand:

• Hazards of the space
• Gas monitor alarms
• Exit procedure
• Communication method
• PPE required
• Work limits
• Emergency signals
• Conditions that require evacuation

Attendant

The attendant remains outside the confined space and monitors the entrant and conditions.

The attendant should not abandon the entry point or enter the space to attempt rescue unless the rescue plan specifically allows it and the attendant is trained and equipped.

Supervisor or Entry Lead

The supervisor or entry lead confirms that the permit, atmospheric testing, isolation, ventilation, rescue plan, equipment and workers are ready before entry.

Competent or Qualified Person

The competent or qualified person performs or reviews the hazard assessment, testing requirements, instrument selection, test interpretation and entry conditions according to the applicable jurisdiction and employer procedure.

CCOHS’s confined-space atmospheric testing guidance repeatedly refers to testing by a competent or qualified person and notes that test interpretation may require knowledge, training and experience with the hazards and equipment.

Confined-Space Testing Checklist

Before entry, confirm:

• The space has been identified and assessed.
• A confined-space plan or procedure is in place.
• Entry permit requirements are complete.
• A competent or qualified person has defined the testing requirements.
• The gas detector is calibrated and bump-tested.
• The detector has the correct sensors for the hazards.
• The pump, probe, tubing and filters are working.
• Oxygen has been checked.
• Flammable gases or vapours have been checked.
• Toxic gases have been checked.
• Multiple levels or locations have been sampled where required.
• Ventilation has been applied where required.
• The space has been retested after ventilation or purging.
• Continuous monitoring is in place where required.
• The entrant has a personal monitor where required.
• Hazardous energy has been isolated or controlled.
• Rescue plan and rescue equipment are ready.
• Communication method is working.
• PPE has been selected.
• Electrical safety controls are in place if electrical work is involved.

Common Confined-Space Measurement Mistakes

Using the Wrong Sensor Package

A four-gas monitor does not detect every possible hazard.

For example, VOCs, ammonia, chlorine or carbon dioxide may require specific sensors.

Skipping the Bump Test

A gas monitor can be calibrated but still fail to respond because of sensor poisoning, blocked filters, damaged tubing or pump problems.

Sampling Only at the Opening

The atmosphere at the opening may not match the atmosphere at the bottom, top or far end of the space.

Ignoring Gas Stratification

Some gases are heavier than air. Others are lighter than air.

Test where the hazard may actually collect.

Assuming Ventilation Solves Everything

Ventilation can change conditions, but pockets of gas may remain. CCOHS warns that toxic gas pockets can remain even when mechanical ventilation is used.

Removing the Personal Monitor After Entry

Conditions can change after workers enter. Keep monitoring as required by the confined-space plan.

Not Accounting for Hot Work

Hot work can consume oxygen, create fumes and introduce ignition sources. CCOHS says oxygen and combustible material concentrations must be monitored during hot work to ensure they remain within the proper range and below applicable lower explosive limit requirements.

Treating Gas Testing as the Whole Safety Plan

Gas testing does not replace isolation, lockout, rescue planning, communication, attendant duties or electrical safety controls.

Canadian Industries Where Confined-Space Testing Matters

Water and Wastewater

Common spaces include:

• Manholes
• Lift stations
• Wet wells
• Digesters
• Pump chambers
• Sewers
• Valve vaults
• Tanks

Hazards may include hydrogen sulphide, methane, oxygen deficiency and biological gases.

Oil and Gas

Common spaces include:

• Tanks
• Process vessels
• Pits
• Separators
• Utility vaults
• Confined process areas

Hazards may include flammable vapours, hydrogen sulphide, VOCs and oxygen deficiency.

Mining

Common spaces include:

• Shafts
• Tunnels
• Equipment compartments
• Tanks
• Bins
• Utility spaces

Hazards may include oxygen deficiency, toxic gases, diesel emissions, poor ventilation and electrical energy.

Utilities and Electrical Contractors

Common spaces include:

• Underground vaults
• Cable chambers
• Manholes
• Transformer vaults
• Utility tunnels
• Switchgear rooms with restricted access

Hazards may include oxygen deficiency, flammable gas, toxic gas, electrical shock, arc flash and difficult rescue conditions.

Manufacturing and Food Processing

Common spaces include:

• Tanks
• Mixers
• Silos
• Vessels
• Ducts
• Ovens
• Pits

Hazards may include cleaning chemicals, oxygen deficiency, combustible dust, vapours and mechanical energy.

Choosing Gas Monitoring Equipment

Before choosing a confined-space gas detector, confirm:

• Which gases must be measured
• Whether oxygen monitoring is required
• Whether LEL monitoring is required
• Which toxic gases are expected
• Whether VOC monitoring is needed
• Whether carbon dioxide monitoring is needed
• Whether remote sampling is needed
• Whether a pump is required
• Hose length and sample delay
• Battery runtime
• Alarm types
• Data logging requirements
• Intrinsic safety or hazardous-location approval
• Calibration gas requirements
• Bump-test process
• Sensor life
• Rental or purchase availability
• Canadian service and support

The RKI Eagle 2 may be appropriate for pumped pre-entry sampling and expanded sensor configurations, while the GX-3R may be appropriate for lightweight personal four-gas monitoring.

Practical Takeaway

Confined-space measurement is not only about taking one gas reading.

A safe process requires:

• Hazard assessment
• Correct gas detector selection
• Calibrated and bump-tested instruments
• Pre-entry atmospheric testing
• Testing at representative locations
• Ventilation and retesting where needed
• Continuous monitoring where required
• Personal monitoring for entrants where required
• Energy isolation and lockout
• Electrical safety controls where electrical work is involved
• A trained attendant
• Communication
• Rescue planning
• Documentation

The source JM Test page recommends the RKI Eagle 2 for initial confined-space testing and RKI personal monitors such as the GX-2009 or GX-3R for ongoing worker monitoring. For Canada, keep this product guidance but add a clear warning that the equipment must be selected and used according to the confined-space plan, manufacturer instructions and the applicable Canadian jurisdictional requirements.

JM Test Systems Canada can support teams with confined-space gas detectors, pumped gas monitors, personal four-gas monitors, calibration gas, bump-test equipment, rentals and calibration support where available. Confirm Canadian inventory, sensor configuration, rental terms, calibration documentation and support before publishing firm claims.