Toxic & Pressurised Gases — Hazardous Chemicals Safety Reference

☠️ Class Overview — Toxic & Pressurised Gases (Cylinders & Tonners)

These gases kill via two distinct mechanisms — direct toxicity (Cl₂, H₂S, CO, phosgene, ClO₂) and simple asphyxiation by oxygen displacement (N₂, and any inert gas in a confined space).
Never enter a confined space (ETP pit, tannery vessel, manhole, N₂-blanketed tank) without a calibrated gas monitor and SCBA on standby — most fatalities in this class are would-be rescuers who entered without protection.
H₂S and CO both cause olfactory fatigue or have no smell at all — never rely on smell as a warning system.
MAH (Major Accident Hazard) and PESO licensing thresholds apply to chlorine, ammonia, phosgene and several others — verify inventory against Schedule quantities under MSIHC Rules 1989.
On-site emergency plans, mock drills, and mutual aid arrangements with neighbouring units are a statutory expectation wherever these gases are stored above threshold.

📑 Jump to a Chemical

Chlorine (Cl₂)Anhydrous Ammonia (NH₃)Hydrogen Sulphide (H₂S)Carbon Monoxide (CO)Sulphur Dioxide (SO₂)Nitrogen (N₂)Oxygen (O₂)Chlorine Dioxide (ClO₂)Phosgene (COCl₂)

Chlorine (Cl₂)

Also known as: Liquefied chlorine gas

Industrial Uses
Water treatment, PVC manufacture, bleach/hypochlorite production, dye intermediates

STORAGE HAZARDS

Store tonners in ventilated locked chlorine shed; keep from ammonia, hydrocarbons; tonner valves corrosion-prone — inspect monthly

HANDLING HAZARDS

TLV-C 1 ppm; IDLH 10 ppm; yellow-green gas, 2.5× heavier than air — sinks into pits/drains; rapid olfactory damage

PROCESS HAZARDS

In damp atmosphere corrodes steel; reacts with ammonia to form explosive NCl₃; corrosive to all elastomers

🛡️ Required PPE — Specific Grades & Types

SCBA — no APR in leak situation
Full chemical suit (Type 1 or Type 3 gastight)
Chemical gloves + boots
On-site escape SCBA for operators

🚨 Emergency Procedure — Large Spill / Major Leak

1	Evacuate 300m downwind — Cl₂ fills low areas
2	Water fog — do NOT jet water on liquid Cl₂
3	Soda ash or caustic soda solution to absorb/neutralise
4	Notify Fire Brigade, DISH, PESO, district authority
5	Medical post for affected persons — delayed pulmonary oedema risk

Anhydrous Ammonia (NH₃)

Also known as: Refrigeration grade ammonia

Industrial Uses
Industrial refrigeration, cold storage, fertilizer plants

STORAGE HAZARDS

MAH threshold 10 MT on-site; PESO licence required; away from oxidisers, acids, chlorine

HANDLING HAZARDS

IDLH 300 ppm; explosive 15–28% in air; dual toxic + flammable hazard

PROCESS HAZARDS

Compressor seal failures common; enclosed engine rooms dangerous; exothermic acid neutralisation

🛡️ Required PPE — Specific Grades & Types

SCBA for any spill
Full chemical coverall acid/alkali resistant
Neoprene gloves and boots
Escape respirator (SCER) for plant operators

🚨 Emergency Procedure — Large Spill / Major Leak

1	Activate site alarm; muster upwind
2	Shut compressor remotely if equipped
3	Water fog to suppress vapour
4	SCBA team attempts valve shutoff
5	Notify DISH, fire brigade, PESO
6	Treat victims: flush eyes 20 min; O₂; call 108

Hydrogen Sulphide (H₂S)

Also known as: Sour gas / rotten egg gas

Industrial Uses
Petrochemical byproduct, tannery/leather effluent, biogas, ETP pits

STORAGE HAZARDS

Process gas — accumulates in ETP tanks, sewer manholes, tannery pits; not stored but forms in situ

HANDLING HAZARDS

Olfactory fatigue at 100–150 ppm — worker smells nothing but is in danger; IDLH 100 ppm; heavier than air

PROCESS HAZARDS

Extremely rapid poisoning — knockdown without warning; explosive 4–44%; reacts with metals

🛡️ Required PPE — Specific Grades & Types

SCBA mandatory for confined space entry
Continuous gas monitor with audible alarm worn by all entrants
Full coverall
Anti-static footwear

🚨 Emergency Procedure — Large Spill / Major Leak

1	Do NOT enter without SCBA — rescuers have died attempting to save victims
2	Drag victim from outside with lifeline
3	Call 108; fresh air; O₂; CPR
4	Ventilate space before any entry
5	Identify and shut off H₂S source

Carbon Monoxide (CO)

Also known as: Silent killer / flue gas

Industrial Uses
Blast furnaces, gas-fired kilns, generator exhaust, boilers, welding

STORAGE HAZARDS

Process gas from incomplete combustion; no colour, odour, or taste — no sensory warning whatsoever

HANDLING HAZARDS

COHb saturation of 50% fatal; symptoms mimic flu — headache, nausea — workers ignore early warning

PROCESS HAZARDS

Diesel generators in enclosed spaces; ceramic kilns; heat treatment furnaces all generate CO

🛡️ Required PPE — Specific Grades & Types

CO personal alarm (electrochemical sensor) — mandatory for hot-work in enclosed areas
SCBA for confined space
No APR effective against CO

🚨 Emergency Procedure — Large Spill / Major Leak

1	Remove victim to fresh air immediately
2	Call 108 — 100% O₂ therapy (hospital hyperbaric O₂ if severe)
3	Do NOT give mouth-to-mouth without own SCBA
4	Ventilate space; confirm <25 ppm before re-entry
5	Identify and shut off combustion source

Sulphur Dioxide (SO₂)

Also known as: Sulphurous anhydride

Industrial Uses
Refrigeration (legacy), dye/paper industry, preservative, sulphonation, ETP

STORAGE HAZARDS

Liquefied gas in tonners; store in ventilated shed away from heat; corrosive to mild steel in presence of moisture

HANDLING HAZARDS

TLV 2 ppm; forms H₂SO₃ and H₂SO₄ on contact with mucous membranes — severe lung damage

PROCESS HAZARDS

Leaks in enclosed dye houses extremely dangerous; reacts with moisture to form acid immediately

🛡️ Required PPE — Specific Grades & Types

SCBA for any leak
Full chemical suit
Neoprene gloves
SO₂ escape respirator at plant entry

🚨 Emergency Procedure — Large Spill / Major Leak

1	Evacuate — SO₂ TLV-C 5 ppm
2	Water fog to absorb/disperse
3	SCBA team shut off tonner valve
4	Soda ash solution to neutralise ground spillage
5	Notify DISH + PESO; medical monitoring for all exposed

Nitrogen (N₂)

Also known as: Inert gas / liquid nitrogen

Industrial Uses
Blanketing tanks, inerting vessels, cryogenic cooling, food packaging

STORAGE HAZARDS

Compressed gas cylinders or cryogenic dewars; cryogenic liquid causes severe frostbite; dry nitrogen displaces O₂ silently

HANDLING HAZARDS

O₂-deficient atmosphere is the main hazard — colourless, odourless, produces euphoria before unconsciousness

PROCESS HAZARDS

Tank blanketing operations; inerting reactors; pipe-pressure testing with N₂ — all create confined space O₂ deficiency risk

🛡️ Required PPE — Specific Grades & Types

O₂ monitor alarm worn by any worker entering N₂-blanketed area
SCBA for emergency entry
Cryogenic gloves for liquid N₂ handling
Face shield for cryogenic handling

🚨 Emergency Procedure — Large Spill / Major Leak

1	Do NOT enter O₂-deficient space without SCBA — victim goes unconscious in seconds
2	Drag victim out with lifeline; fresh air; CPR
3	Ventilate confined space before entry
4	For cryogenic LN₂ spill: allow to vaporise in ventilated area; cryogenic burns — flush with warm water

Oxygen (O₂)

Also known as: Compressed/medical oxygen

Industrial Uses
Welding, cutting, medical use, combustion enhancement, wastewater treatment

STORAGE HAZARDS

Strong oxidiser — dramatically accelerates fire; segregate from flammables, greases, oils; store cylinders away from heat in ventilated area

HANDLING HAZARDS

Oil/grease contact with pure O₂ can be spontaneously explosive; enriched atmosphere makes fires burn faster and hotter

PROCESS HAZARDS

Oxygen-enriched atmospheres in welding areas; O₂ concentrators for ETP aeration

🛡️ Required PPE — Specific Grades & Types

No oil or grease on gloves/tools when handling O₂ equipment
Clean cotton gloves only
No synthetic fabrics in O₂-rich environments
Welding shield for oxy-fuel cutting

🚨 Emergency Procedure — Large Spill / Major Leak

1	O₂-enriched fire: no organic extinguishing agents; large volumes of water
2	Shut off O₂ valve immediately
3	Remove all ignition sources and combustibles
4	No synthetic clothing in O₂-enriched area — burns violently
5	Ventilate area before re-entry

Chlorine Dioxide (ClO₂)

Also known as: Alcide / Oxine

Industrial Uses
Bleaching (paper/textiles), water treatment, disinfection

STORAGE HAZARDS

Extremely unstable — explosive above 10% concentration; typically generated on-site; cylinders rarely used

HANDLING HAZARDS

Extremely toxic oxidiser; TLV 0.1 ppm; decomposes to Cl₂ and O₂ on contact with organics

PROCESS HAZARDS

On-site generation from NaClO₂ + acid; equipment corrosion and pressure buildup dangerous

🛡️ Required PPE — Specific Grades & Types

SCBA for any ClO₂ generation area
Full chemical suit
Chemical goggles + gloves

🚨 Emergency Procedure — Large Spill / Major Leak

1	Evacuate immediately — extreme toxicity and explosion risk
2	SCBA team only for response
3	Notify DISH + fire services
4	No attempt to confine or contain without fully enclosed PPE suite

Phosgene (COCl₂)

Also known as: Carbonyl chloride

Industrial Uses
Pharma isocyanate intermediates, specialty chemicals (very limited SME use)

STORAGE HAZARDS

Highly toxic liquefied gas; MAH substance; PESO licence required; minimal storage quantities

HANDLING HAZARDS

Insidious — delayed pulmonary oedema 6–24 hr after exposure; TLV-C 0.02 ppm; smells like fresh hay at low conc.

PROCESS HAZARDS

Hydrolysis generates HCl; reaction with amines is violent; exposure during cylinder change most dangerous

🛡️ Required PPE — Specific Grades & Types

SCBA — absolutely no APR
Full Type 1 encapsulating suit
Chemical gloves + boots

🚨 Emergency Procedure — Large Spill / Major Leak

1	Medical emergency — call 108; delayed oedema means NO symptoms initially
2	Admit victim for 24 hr hospital observation even if feeling well
3	SCBA rescue team; full site evacuation
4	Notify DISH, PESO, SPCB, district authority immediately