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What Is a Confined Space?

PEOPLE DIE IN CONFINED SPACES EVERY YEAR. Most fatalities occur during rescue attempts by untrained colleagues who enter without breathing apparatus. NEVER enter a confined space without a safe system of work in place. NEVER attempt rescue without SCBA.

Legal Definition — Confined Spaces Regulations 1997, Reg 1(2)

A confined space is any place which is substantially (though not always entirely) enclosed, and where serious injury can occur from hazardous substances or conditions within the space or nearby.

Two conditions must both be met:

  1. The space is substantially enclosed (not necessarily totally sealed)
  2. There is a reasonably foreseeable risk of serious injury from conditions or substances in or near the space

A space does not need to be small or difficult to access to be "confined" — a large furnace chamber with restricted ventilation qualifies.

Furnace Confined Spaces

The following are commonly encountered confined spaces in furnace service work:

Space Why It Is Confined Specific Hazards
Furnace chamber / retort Enclosed vessel, restricted opening, limited ventilation Residual atmosphere (N2, CO, H2, NH3), heat, graphite dust, ceramic fibre
Vacuum furnace hot zone Sealed vessel, single access door Argon pooling (heavier than air), graphite dust, residual vacuum oils
Quench tank / oil pit Below-ground vessel, restricted egress Oil vapours, O2 depletion, heat, slippery surfaces, drowning risk
Heat exchanger / recuperator Tube bundle enclosure, restricted access Residual flue gases (CO, CO2), soot, heat
Flue system / chimney Vertical or horizontal duct, restricted access CO, CO2, soot, heat, restricted movement
Salt bath vessel Deep vessel, restricted access from above Cyanide salts (HCN gas), residual heat, fume
Pit furnace (below ground) Depth, single top access, restricted egress Heavy gas accumulation (Ar, CO2), heat, fall hazard
Generator (endo/exo) Retort interior, restricted opening Catalyst dust (Ni), CO, residual atmosphere
Sealed quench vestibule Enclosed chamber between furnace and quench CO, H2, oil vapours, N2, heat
Remember: A furnace that has been purged with nitrogen or argon may look perfectly safe — the air appears normal, there is no smell, no visible hazard. But entering that space without checking oxygen levels will cause unconsciousness in seconds and death in minutes.

Atmospheric Hazards

ATMOSPHERIC HAZARDS ARE THE NUMBER ONE KILLER IN CONFINED SPACES. Most furnace-related confined space deaths are caused by oxygen depletion from residual nitrogen or argon purge gas. These gases are odourless, colourless, and give ZERO warning.

Gases Encountered in Furnace Work

Gas Formula Type WEL / TWA STEL IDLH Properties Furnace Source
Nitrogen N2 Asphyxiant Simple asphyxiant — — Odourless, colourless, SG 0.97. INVISIBLE KILLER. Purge gas, protective atmosphere, nitriding, vacuum backfill
Carbon Monoxide CO Toxic + Flammable 20 ppm 100 ppm 1200 ppm Odourless, colourless, SG 0.97. Binds to haemoglobin (COHb). Endothermic gas (20% CO), combustion products, sealed quench
Hydrogen H2 Flammable Simple asphyxiant — — LEL 4%, UEL 75%. Invisible flame. SG 0.07 (very light). Endothermic gas (40% H2), bright annealing, brazing
Ammonia NH3 Toxic + Corrosive 25 ppm 35 ppm 300 ppm Pungent smell, lighter than air (SG 0.59), corrosive to eyes and lungs. Nitriding furnaces, carbonitriding
Hydrogen Cyanide HCN Extremely Toxic 0.9 ppm 4.5 ppm 50 ppm Bitter almond smell (not all can detect). Rapidly fatal. SG 0.94. Cyanide salt baths, spent nitriding atmospheres
Methanol CH3OH Toxic + Flammable 200 ppm 250 ppm 6000 ppm Sweet smell. Toxic by inhalation and skin absorption. LEL 6%. Nitrogen-methanol atmosphere systems
Quench oil vapours Various Flammable + Irritant 5 mg/m³ (oil mist) 10 mg/m³ — Hydrocarbon vapours, respiratory irritant, fire risk. Quench tanks, sealed quench vestibules, oil pits
Carbon Dioxide CO2 Asphyxiant 5000 ppm 15000 ppm 40000 ppm Odourless at low concentration, heavier than air (SG 1.52). Combustion products, exothermic gas, carbonitriding exhaust
Argon Ar Asphyxiant Simple asphyxiant — — Odourless, colourless, SG 1.38 — HEAVIER THAN AIR, pools in low points. Vacuum furnace backfill, reactive metal processing, welding purge
Oxygen depletion O2 Life Threat 19.5% min — <16% Normal air is 20.9%. Below 19.5% is DANGEROUS. Below 16% causes impaired judgement. Below 6% is fatal. Any purged or inerted furnace, any space with gas leaks
NITROGEN KILLS WITHOUT WARNING. Breathing pure N2 causes unconsciousness in 1-2 breaths and death in 3-4 minutes. There is no sensation of suffocation — victims simply collapse. A furnace purged with nitrogen looks, smells, and feels exactly like normal air. Always test O2 levels before entry. Always.

Carbon Monoxide — Symptoms by Concentration

CO Level (ppm) COHb % Symptoms Time to Effect
20 3-4% No symptoms (UK WEL TWA) —
50 7-8% Mild headache 2-3 hours
100 12-15% Headache, dizziness (UK STEL) 1-2 hours
200 20-25% Severe headache, confusion, nausea 1-2 hours
400 35-40% Life-threatening, collapse 1-2 hours
800 50-60% Unconsciousness, convulsions 15-45 minutes
1600 60-70% Death Under 30 minutes
6400+ 80%+ Immediate collapse, death in minutes 1-3 minutes
Endothermic gas is 20% CO. That is 200,000 ppm. A furnace filled with endo gas is immediately lethal. Even a small leak from a poorly sealed furnace door can create lethal CO concentrations in the working area. Always wear a personal CO monitor when working near atmosphere furnaces.

Oxygen Depletion Effects

O2 Level Effect
20.9%Normal air
19.5%MINIMUM safe level for entry (OSHA/HSE)
16-19%Reduced coordination, impaired judgement, increased heart rate
12-16%Breathing difficulties, poor judgement, muscular weakness
10-12%Nausea, vomiting, unable to move freely, may lose consciousness
6-10%Loss of consciousness within minutes, death if not rescued
<6%Immediate loss of consciousness (1-2 breaths), death within minutes

Atmospheric Monitoring

NEVER trust your senses. You cannot see, smell, or feel oxygen depletion. You cannot see or smell nitrogen. You cannot smell carbon monoxide. By the time you feel unwell, it may already be too late to escape. ALWAYS use calibrated gas detection equipment.

Minimum Requirement: 4-Gas Detector

The minimum acceptable instrument for confined space entry measures four gases simultaneously:

Sensor Measures Why It Matters for Furnace Work
O2 Oxygen 0-25% Detects O2 depletion from N2, Ar, or any inert gas purge
LEL Combustible gases 0-100% LEL Detects H2, natural gas, oil vapours, methanol
CO Carbon monoxide 0-999 ppm Detects residual endo/exo gas, incomplete combustion
H2S Hydrogen sulphide 0-100 ppm Detects quench oil decomposition gases, sewer gas in pits

Additional sensors for furnace work: NH3 (nitriding), HCN (salt baths), CO2 (flue entry).

Testing Sequence — ORDER MATTERS

1
Test O2 FIRST. If oxygen is depleted, the LEL sensor will give false readings (catalytic sensors need O2 to work). O2 must be 19.5-23.5% before proceeding.
2
Test LEL (combustibles). Must read 0% LEL (or below 10% LEL maximum with forced ventilation and continuous monitoring). If above 10% LEL, do NOT enter.
3
Test toxic gases (CO, H2S, NH3, HCN as applicable). All must be below WEL before entry without RPE. If above WEL but below IDLH, entry with appropriate RPE may be considered.
4
Test at multiple levels. Top, middle, and bottom of the space. Heavy gases (Ar, CO2) pool at the bottom. Light gases (H2) rise to the top. Use a sampling pump with extension hose.
5
Continuous monitoring during entry. Wear the detector on your person at breathing height. Set alarms to TWA and STEL levels. If any alarm sounds, evacuate immediately.

Gas Detector Action Levels

Parameter Safe for Entry Alert / Caution Evacuate Immediately
O2 19.5 – 23.5% <19.5% or >23.5% <18% or >23.5%
LEL 0% >5% LEL >10% LEL
CO <20 ppm 20-35 ppm (TWA alarm) >100 ppm (STEL alarm)
H2S <5 ppm 5-10 ppm (TWA alarm) >10 ppm (STEL alarm)
NH3 <25 ppm 25-35 ppm >35 ppm
HCN <0.9 ppm 0.9-4.5 ppm >4.5 ppm

Equipment

Common Gas Detectors for Furnace Work

Model Gases Features Notes
Honeywell BW MicroClip XL/X3 O2, LEL, CO, H2S Compact, rugged, IntelliFlash compliance indicators Industry standard. Good all-round unit.
Dräger X-am 2500/5000 Up to 5 gases (configurable) Optional pump module, datalogging, ATEX rated X-am 5000 accepts NH3 and HCN sensors.
MSA Altair 4X/5X O2, LEL, CO, H2S (+ optional) MotionAlert (man-down), InstantAlert (manual alarm) Altair 5X supports PID sensor for VOCs.
Bump test DAILY. Before each use, expose the detector to a known concentration of calibration gas. This confirms sensors are responding. A detector that has not been bump tested is NOT reliable. Full calibration at least every 6 months (or per manufacturer schedule). Keep calibration records.
Catalytic LEL sensors are POISONED by silicones. Silicone sealants, silicone spray, PTFE tape with silicone, and some cleaning agents will permanently damage the sensor. It will read zero even in the presence of flammable gas. If silicones are present in the work area, use an infrared (IR) LEL sensor instead.

Safe System of Work

CSR 1997 Reg 4 requires a safe system of work for all confined space entry. The following 13-step procedure covers furnace service entry:

1
Risk Assessment. Site-specific assessment for this space, this task, this day. Consider: what atmosphere was in the furnace? When was it last run? What process gases were used? Is there residual heat? Is there an oxygen-free atmosphere? Review previous entry records.
2
Permit to Enter. Formal written permit issued by a competent authorised person. Specifies hazards, precautions, time limits, and emergency procedures. See the Permit section below.
3
Lockout / Tagout (LOTO). Electrically isolate all heating elements, fans, conveyors, door mechanisms, and atmosphere control systems. Padlock all isolators. Personal locks — each entrant applies their own lock. Tags with name, date, and reason.
4
Cool Down. Verify internal temperature is below 35°C (safe working limit for sustained work). Use thermocouple or infrared thermometer at multiple points including floor, walls, and any residual workload. Allow additional cooling time for refractory-lined furnaces which retain heat for extended periods.
5
Purge / Ventilate. If the furnace contained a protective atmosphere (N2, H2, endo, Ar), purge with air. Open all doors and ports. Use forced ventilation (fan/blower) to establish airflow through the space. Minimum 5 volume changes of fresh air.
6
Atmospheric Testing. Test at multiple levels (top, middle, bottom) using calibrated 4-gas detector with sampling pump. O2 first, then LEL, then toxics. ALL readings must be safe before entry. Record results on permit.
7
Continuous Ventilation. Maintain forced ventilation throughout entry. Position fan to blow fresh air INTO the space (positive pressure). Exhaust should vent to a safe area (not into the workshop if toxic gases present).
8
Rescue Equipment in Position. SCBA (self-contained breathing apparatus), rescue harness with lifeline, tripod/davit arm with rescue winch positioned at entry point. First aid kit including oxygen therapy unit. All equipment checked and ready to use.
9
Rescue Team Standing By. Minimum one trained rescue person stationed at the entry point at all times. This person does NOT enter the space. They maintain visual and verbal contact with the entrant. They are trained in SCBA use and rescue procedures.
10
Communications. Establish and test communication between entrant, standby person, and supervisor. Voice, hand signals, or radio. Agree check-in intervals (maximum 5 minutes for high-risk spaces). Agree emergency signal (3 blasts on whistle, or continuous siren).
11
Entry. Entrant wears continuous gas monitor at breathing height. Wears rescue harness with lifeline attached. Carries portable lighting (intrinsically safe if flammable atmosphere possible). Signs entry log with time in.
12
Regular Check-Ins. Standby person checks with entrant at agreed intervals. If no response within 2 check-in intervals, initiate emergency procedure immediately. Monitor atmospheric readings continuously.
13
Exit and Permit Closure. Entrant exits, removes personal lock. Signs out on entry log with time out. Competent person inspects space, closes permit. Remove ventilation only after all work confirmed complete. Record all atmospheric readings taken during entry.
SHORTCUTS KILL. Every step exists because someone died when it was skipped. "It'll only take a minute" and "I've done this a hundred times" are the last words of too many engineers. If any step cannot be completed, do NOT enter. Re-assess and re-plan.

Permit to Enter

What the Permit Must Contain

  • Description and location of the confined space
  • Name of the competent person issuing the permit
  • Purpose of entry and work to be carried out
  • Identified hazards and control measures
  • Atmospheric test results (O2, LEL, CO, others as applicable) with time of test
  • Isolation details (electrical, gas, mechanical) with lock/tag numbers
  • Ventilation arrangements
  • PPE and RPE requirements
  • Communication method and check-in intervals
  • Emergency and rescue arrangements
  • Names of all entrants and standby personnel
  • Time of entry and maximum duration
  • Signature of issuing authority, entrant(s), and standby person

Permit Rules

Duration:

Maximum one shift. A new permit must be issued for each shift, even if the work is continuing. If conditions change significantly during a shift (e.g., weather, process restart nearby), cancel and re-issue.

Handover:

If work spans shifts, a formal handover must occur. Outgoing permit is cancelled, incoming authorised person re-assesses, re-tests atmosphere, and issues a new permit. Atmospheric conditions can change overnight.

Cancellation:

The permit must be cancelled (not just closed) if: any alarm sounds, conditions change, the scope of work changes, an emergency occurs, or the standby person must leave their post. A new permit is required to resume entry.

Authority:

Only a competent authorised person may issue a confined space permit. This person must have completed confined space training, understand the hazards, and have the authority to stop work. The entrant cannot authorise their own permit.

Isolation Requirements

ISOLATION SAVES LIVES. Before anyone enters a furnace, ALL energy sources must be positively isolated, locked out, and verified. Electrical, gas, mechanical, and process atmosphere supplies — ALL of them. No exceptions.

Electrical Isolation

LOTO Required
  • Main isolator: Open and padlock in OFF position. Use personal lock with unique key.
  • Local isolator: Open and padlock if separate from main.
  • Stored energy: Discharge capacitors (SCR/thyristor controllers may retain charge). Verify zero energy with voltage tester.
  • Elements: Verify element resistance shows open circuit or de-energised state. Graphite elements can retain residual charge.
  • Fans/motors: Isolate separately. Circulation fans, cooling fans, quench agitators.
  • Door mechanisms: Isolate hydraulic, pneumatic, or electric door operators. Mechanically secure doors in open position with props/chains.
  • Try-test: After LOTO, attempt to start the equipment from the normal control panel. It must NOT respond. This confirms isolation is effective.

Gas Isolation

Double Block & Bleed
  • Double block and bleed: Close two valves in series on the gas supply and open a vent valve between them. This is the ONLY acceptable method for confined space gas isolation. A single valve is NOT sufficient.
  • Applies to: Natural gas, LPG, nitrogen, hydrogen, argon, ammonia, endothermic gas, exothermic gas — ALL gas supplies.
  • Vent to safe location: The bleed vent must discharge to a safe area outdoors, away from ignition sources and air intakes.
  • Verify: Check downstream pressure gauge reads zero. Listen for leakage at bleed vent (should be silent after initial depressurisation). If in doubt, use soap solution on joints.
  • Spectacle blinds / spades: For highest integrity isolation, install a spectacle blind (spade) in the pipeline. This provides a physical barrier against gas passing the isolation point.

Mechanical Isolation

  • Doors: Mechanically secure in the open position. Use chains, props, or dedicated door locks. Do NOT rely on hydraulic/pneumatic pressure to hold doors open — pressure can fail.
  • Conveyors and roller hearths: Isolate drive motors. Engage mechanical brakes or insert physical stops. Verify rollers cannot move.
  • Quench elevators/lifts: Isolate hydraulic power pack. Lower platform to bottom. Insert mechanical safety pins.
  • Rotating equipment: Fans, recirculating pumps, agitators — isolate, lock, and verify stationary.

Process Atmosphere Isolation

  • Nitrogen supply: Isolate at source (bulk tank valve or manifold). Double block and bleed at furnace connection. Verify with pressure gauge.
  • Hydrogen supply: Isolate at cylinder manifold. Close cylinder valves. Double block and bleed at furnace. Purge residual H2 with N2, then purge N2 with air.
  • Ammonia supply: Isolate at cylinder/tank. Purge with N2. Verify with NH3 detector. Handle with extreme care — NH3 is corrosive and toxic.
  • Endothermic/exothermic generators: Shut down generator. Isolate gas supply to generator. Isolate generator output to furnace. Purge with N2 then air.
  • Vacuum system: Close gate valve. Isolate pump. Vent furnace to atmosphere through a safe route.

Rescue & Emergency

NEVER ATTEMPT RESCUE WITHOUT SCBA. The single greatest cause of multiple fatalities in confined spaces is would-be rescuers entering without breathing apparatus. If your colleague collapses in a confined space, the atmosphere that incapacitated them WILL incapacitate you too. Raise the alarm. Put on SCBA. Then — and ONLY then — enter to rescue.
CASCADE RESCUE DEATHS. Time and again, investigations find that for every 1 person who dies in a confined space, 1-2 more die trying to rescue them without breathing apparatus. This is preventable. Training and discipline save lives.

Rescue Plan Requirements

The rescue plan must be in place before entry begins. It must include:

  • Identified rescue team members and their roles
  • Method of raising the alarm (whistle, radio, siren)
  • Method of communication with emergency services (phone, location details)
  • Method of extracting a casualty (harness + winch, stretcher, manual lift)
  • First aid provisions including oxygen therapy
  • Location of nearest A&E with details provided to 999 operator

Rescue Equipment

Equipment Purpose Requirement
SCBA (Self-Contained Breathing Apparatus) Provides breathable air independent of ambient atmosphere Minimum 2 sets at entry point. Rescuer must be trained and face-fit tested. Typical cylinder duration 30-45 minutes.
Rescue harness with D-ring Allows casualty to be lifted vertically Worn by all entrants. Dorsal D-ring for vertical lift. Must be compatible with winch/tripod.
Tripod / davit arm Overhead anchor point for rescue winch Positioned over entry point. Rated for rescue loads (minimum 140 kg). Tripod for top-entry; davit for side-entry.
Rescue winch / inertia reel Mechanical advantage for lifting casualty Man-riding rated. Tested and certified. Connects to harness D-ring via lifeline.
Lifeline Connection between entrant and anchor/winch Must not create entanglement hazard inside space. Consider retractable type.
Oxygen therapy unit Administer oxygen to rescued casualty Demand valve with mask. Only trained first aiders to administer. Do NOT use in flammable atmosphere.
Stretcher (confined space type) Immobilise and extract casualty through restricted openings Flexible/folding type (e.g., SKED, Paraguard). Standard rigid stretchers may not fit through furnace doors.
RESCUE DRILL REQUIREMENT. Practice rescue procedures regularly — at least every 6 months for regular entrants. A rescue plan that has never been practised is not a rescue plan. Time yourself — a casualty in a zero-oxygen atmosphere has approximately 4 minutes before brain damage begins.

Specific Furnace Scenarios

Each furnace type presents unique confined space hazards. The following scenarios cover the most common situations encountered by Bloor Engineering service engineers.

Vacuum Furnace Hot Zone

High Risk

Hazards

  • Argon pooling: Ar (SG 1.38) is heavier than air and pools at the bottom of the chamber. After backfilling with Ar, the lower portion of the hot zone may contain zero oxygen even with the door open. You can be standing in breathable air at head height while your feet are in a lethal atmosphere.
  • Graphite dust: Graphite felt, board, and element erosion creates fine carbon dust. Respiratory irritant. Use FFP3 mask minimum. Graphite dust is also combustible in suspension.
  • Residual vacuum pump oils: Diffusion pump fluid (DC705, Santovac) residue on cold surfaces. Low toxicity but irritant.
  • Confined geometry: Many hot zones require crouching or lying inside. Restricted movement hampers self-rescue.

Specific Precautions

  • After Ar backfill: open door fully, ventilate with fan for minimum 30 minutes before atmospheric testing
  • Test O2 at FLOOR LEVEL inside the chamber — this is where Ar settles
  • Maintain continuous forced ventilation during hot zone work
  • Wear FFP3 mask for graphite dust protection
  • If hot zone is deep (walk-in type), treat as full confined space entry with permit, SCBA standby, and rescue plan
ARGON IS AN INVISIBLE KILLER. Because argon is 38% heavier than air, it does not readily disperse. It pools in the bottom of vessels and pits like an invisible liquid. Multiple fatalities have occurred in the heat treatment industry from engineers entering argon-filled chambers. A gas detector worn at chest height may read normal O2 while the atmosphere at knee level is lethal. Always test at multiple levels.

Sealed Quench Furnace

Multiple Hazards

Hazards

  • Residual CO and H2: Endothermic gas (20% CO, 40% H2) remains in the furnace and vestibule after shutdown. CO is immediately lethal at these concentrations.
  • Oil vapours: Quench oil (flash point typically 170-200°C) produces hydrocarbon vapours. These are flammable and respiratory irritants. Cold oil surfaces may still evolve vapours if contaminated with dissolved gases.
  • Quench tank depth: Oil tanks are typically 1-2m deep. Drowning risk if engineer falls in during maintenance. Oil-covered surfaces are extremely slippery.
  • Nitrogen blanket: Some sealed quench furnaces have N2 blanket over the oil. This O2-depleted zone extends above the oil surface.

Specific Precautions

  • After shutdown: purge furnace chamber and vestibule with N2, then air. Minimum 10 volume changes of air.
  • Open all doors, inspection ports, and burner ports for cross-ventilation
  • Test CO specifically — it lingers in porous insulation and can off-gas for hours
  • For oil tank entry: drain oil, ventilate tank, test for LEL and O2, use non-sparking tools
  • Install fall arrest at quench tank opening during maintenance

Nitriding Retort

Toxic Atmosphere

Hazards

  • Residual ammonia (NH3): WEL 25 ppm TWA. Pungent smell at low levels, but high concentrations cause olfactory fatigue (you stop smelling it). Corrosive to eyes, skin, and lungs. 300 ppm is IDLH.
  • Dissociated ammonia: At process temperature, NH3 decomposes to N2 + H2. On cooling, residual atmosphere is a mixture of NH3, N2, and H2 — toxic, asphyxiant, AND flammable.
  • White powder residue: Iron nitride dust on surfaces. Respiratory irritant.

Specific Precautions

  • Purge retort thoroughly with N2 then air after shutdown. NH3 adsorbs onto metal surfaces and releases slowly.
  • Use NH3-specific gas detector (4-gas monitor does NOT detect NH3 unless fitted with optional sensor)
  • Wear chemical splash goggles and RPE (minimum FFP3; full-face respirator with ammonia cartridge for levels >25 ppm)
  • Have water available for eye/skin decontamination
  • Ventilate for extended period — NH3 takes much longer to clear than N2 or CO

Salt Bath Vessel

Extreme Hazard

Hazards

  • Cyanide salts: Carburizing and carbonitriding salt baths contain sodium or potassium cyanide. Contact with acid (even weak acid or CO2 in air) generates HCN gas — WEL 0.9 ppm, IDLH 50 ppm. Rapidly fatal at higher concentrations.
  • Skin absorption: Cyanide salts are toxic through skin contact, not just inhalation. Gloves, coveralls, and face protection essential.
  • Residual salt on surfaces: Dried salt crust on walls and fittings remains toxic. Water contact can generate HCN from cyanide residues.
  • Depth: Salt bath vessels are typically 1-2m deep. Fall risk with limited egress.
CYANIDE IS ONE OF THE MOST DANGEROUS SUBSTANCES IN HEAT TREATMENT. HCN gas is detectable by smell ("bitter almonds") in some people, but approximately 40% of the population cannot smell it. At concentrations above 50 ppm, death can occur within minutes. Specific HCN detection equipment is MANDATORY. Standard 4-gas monitors do NOT detect HCN.

Specific Precautions

  • HCN-specific gas detector (electrochemical sensor, 0-30 ppm range minimum)
  • Full-face respirator with cyanide-rated cartridge (Type B or BK) for residual levels. SCBA for entry if levels unknown.
  • Cyanide antidote kit immediately available (hydroxocobalamin or Cyanokit). First aiders trained in administration.
  • Wash facilities immediately adjacent. Emergency shower and eye wash within 10 seconds travel.
  • All waste (PPE, cloths, residue) treated as hazardous waste. Cyanide-containing waste must NOT be mixed with acids.

Flue Systems & Chimneys

Toxic + Restricted

Hazards

  • CO and CO2: Residual combustion gases. CO lingers in poorly ventilated flue sections. CO2 (heavier than air) pools in horizontal runs and at the base of vertical stacks.
  • Soot: Carbon deposits. Respiratory irritant, potential PAH (polycyclic aromatic hydrocarbon) exposure. COSHH assessment required.
  • Heat: Refractory-lined flues retain heat for extended periods after furnace shutdown.
  • Restricted access: Flue runs are typically 300-900mm diameter. Very difficult to self-rescue or to extract a casualty.

Specific Precautions

  • Cool for minimum 24 hours after furnace shutdown (refractory retention)
  • Forced ventilation through the full length of the flue
  • Test at multiple points along the run, not just at the access point
  • Lifeline attached at all times. Rescue plan must account for restricted diameter.
  • FFP3 mask minimum for soot. Consider powered air-purifying respirator (PAPR) for extended work.

Pit Furnace (Below Ground)

Multiple Hazards

Hazards

  • Depth: Pit furnaces range from 1m to 10m+ deep. Single top access only. Fall from height risk during access/egress.
  • Heavy gas accumulation: Ar, CO2, and quench oil vapours (all heavier than air) accumulate at the bottom of the pit. Natural ventilation is extremely poor in below-ground spaces.
  • Limited egress: Only exit is upward. If you are incapacitated at the bottom, rescue is difficult. Ladder access only — cannot carry a casualty up a ladder.
  • Heat retention: Below-ground refractory retains heat longer than above-ground furnaces. Surrounding soil acts as insulation.
  • Water ingress: Groundwater can accumulate in pit furnaces, creating drowning risk, electrical risk (if elements still connected), and steam risk if hot surfaces present.

Specific Precautions

  • Tripod and rescue winch positioned directly over pit opening
  • Harness worn by all entrants with lifeline attached to winch
  • Test atmosphere at bottom of pit (use sampling pump with extension tube lowered on rope)
  • Forced ventilation directed to bottom of pit (heavy gases must be physically displaced upward)
  • Fall arrest installed at pit edge. Guardrails around pit opening when cover removed.
  • Safe means of access (secured ladder, or crane-lowered platform for deep pits)
PIT FURNACES ARE AMONG THE HIGHEST-RISK CONFINED SPACES. They combine depth, restricted egress, heavy gas accumulation, and difficult rescue into a single hazard. Always treat pit furnace entry as a high-risk confined space operation requiring the full 13-step procedure, rescue team, tripod/winch, and SCBA standby.

Training & Records

Training Requirements

All persons involved in confined space work must be competent. Competence means having sufficient training, experience, knowledge, and other qualities to carry out the work safely.

Role Training Required Refresher Interval
Entrant Confined space awareness. Hazard recognition. Use of gas detector. Emergency procedures. Use of rescue harness. Every 3 years (theory), annual refresher (practical)
Standby / Top Person All entrant training PLUS: rescue procedures, SCBA donning and use, winch/tripod operation, casualty extraction, emergency communication. Every 3 years (theory), annual refresher (practical with SCBA)
Permit Issuer / Authorised Person All standby training PLUS: risk assessment, permit writing, isolation procedures, atmospheric monitoring and interpretation, regulatory knowledge (CSR 1997, L101). Every 3 years (theory), annual refresher
Rescue Team Member All standby training PLUS: advanced rescue techniques, casualty handling in confined spaces, use of stretcher in restricted access, oxygen therapy administration. Every 3 years (theory), 6-monthly practical drills
Gas Detector User Operation of specific instrument model. Bump testing. Calibration. Sensor limitations. Interpretation of readings. Cross-sensitivity. Annual, plus whenever a new instrument model is introduced
SCBA Wearer Donning and doffing. Pre-use checks. Duration management. Face-fit testing. Working in SCBA. Communications while wearing. Annual practical, face-fit test every 3 years (or if face shape changes)

Record Keeping

The following records must be maintained:

  • Permits to enter: Retain completed permits for minimum 3 years. Include all atmospheric test results, names of entrants, times, and any incidents.
  • Risk assessments: Retain for minimum 3 years. Review and update annually or when conditions change.
  • Training records: Retain for the duration of employment plus 3 years. Include certificate dates, trainer details, competency assessments.
  • Gas detector calibration records: Retain for the life of the instrument plus 1 year. Include bump test logs, full calibration dates, sensor replacement dates.
  • Equipment inspection records: SCBA service records, harness inspection dates, tripod/winch certification, lifeline test records.
  • Incident and near-miss reports: Retain indefinitely. Investigate all near-misses — they are warnings of future fatalities.
HSE inspectors WILL ask for records. Following any incident, the HSE will request permits, risk assessments, training records, and calibration logs. If you cannot produce these records, the legal presumption is that the work was not done safely. Good records demonstrate good practice and provide your primary defence.
THIS PAGE IS A REFERENCE — NOT A SUBSTITUTE FOR TRAINING. Confined space entry is one of the most hazardous activities in furnace service work. Every person who enters a confined space, acts as a standby, or issues a permit must have received formal training from a competent training provider. Reading this page does not make you competent. Get trained. Stay trained. Stay alive.