Chemicals, Gases and Welding
Safety data sheets, solvents and adhesives, compressed gas cylinders, oxygen and carbon dioxide hazards, welding and cutting.
Reading a safety data sheet and a label
Every chemical product comes with a safety data sheet (SDS), a 16-section document from the maker. Reading the few key sections takes two minutes and tells you the hazards, the protective equipment and what to do in an emergency.
| Section | What to look for |
|---|---|
| 2. Hazard identification | Pictograms, signal word (danger or warning), hazard statements (for example “flammable”, “causes serious eye damage”) |
| 4. First-aid measures | What to do after skin, eye, inhalation or swallowing |
| 5. Fire-fighting | Suitable extinguisher; hazardous combustion products |
| 7. Handling and storage | Ventilation, incompatible materials, temperature limits |
| 8. Exposure controls and PPE | Exposure limits, respirator and glove type |
| 9. Physical and chemical properties | Flash point, vapor pressure, explosive limits |
| 10. Stability and reactivity | What it must not be mixed with |
| 13. Disposal | How to throw it away |
- Pictograms: a flame (flammable), exclamation mark (irritant), corrosion (burns metals and skin), skull and crossbones (acute toxic), health hazard (cancer, organ damage), gas cylinder (gas under pressure), flame over circle (oxidizer), exploding bomb, environment.
- Keep the SDS for every product in a folder or on your phone, and re-read it when you change product: brands differ.
- Label every container you decant into; an unlabeled bottle is a poisoning waiting to happen.
Solvents, adhesives and finishes
Solvent vapors dissolve into the body through the lungs and skin, and many damage the nervous system, liver or kidneys. They are also flammable (see Fire, Fuels and Explosion). The exposure limit is given in parts per million (ppm) of vapor in the air.
Worked example: 100 mL evaporating in a small shop
One hundred milliliters of each liquid evaporating in a 50 m³ closed room gives:
| Solvent | Typical limit | Concentration reached | Times the limit |
|---|---|---|---|
| Acetone | 250 ppm | 665 ppm | 2.7 × |
| Toluene | 20 ppm | 462 ppm | 23.1 × |
| Isopropyl alcohol | 400 ppm | 640 ppm | 1.6 × |
| Mineral spirits | 100 ppm | 254 ppm | 2.5 × |
- Toluene reaches 462 ppm: 23 times a limit of 20 ppm (illustrative). The air needed to keep one 100 mL spill below the limit is 1 155 m³: 23 times the room volume.
- Acetone and alcohol have much higher limits but burn at lower concentrations (see the fire page): the explosive limit is the hazard.
- Smell is not a safe guide: you adapt to a smell within minutes and many dangerous vapors are noticed only well above their limits.
- At a use of 100 mL an hour of toluene, keeping the room at the 20 ppm limit by dilution would need about 19 m³/min of fresh air (23 air changes an hour): use a spray booth or an extraction hood, and switch to a safer product (see Dust, Fumes and Ventilation).
- Substitute: water-based finishes, adhesives and cleaners where they will do the job.
- Use small quantities, keep lids on, work outdoors or at an open door with a fan drawing air away from you.
- Protect skin: nitrile gloves (check the chemical resistance: some solvents go straight through), long sleeves.
- Respirator: an organic-vapor cartridge for short, light use; supplied air for spraying isocyanate paints (see Personal Protective Equipment).
- Epoxies and polyurethanes sensitize: after a few exposures you can become allergic for life. Avoid skin contact from the first time.
- No eating, drinking or smoking where chemicals are used; wash hands before.
Never mix, and store apart
| Do not mix | What happens |
|---|---|
| Bleach + ammonia (glass cleaner) | Chloramine gas: eyes, lungs |
| Bleach + acid (rust remover, toilet cleaner) | Chlorine gas |
| Acid + metal (aluminum, zinc) | Hydrogen gas: fire, explosion |
| Oxidizer (nitrate, peroxide) + fuel or oil | Fire, explosion |
| Chlorinated solvent + welding arc | Phosgene gas |
| Isocyanate + moisture or amine | Heat, foam, toxic aerosols |
| Cyanoacrylate + cotton or wool cloth | Heat and smoke in seconds |
Worked example: how much can you store?
- Keep only what you need for the job: a 5 liter can of thinner is already a hazard; a 450 liter flammable-liquids cabinet is the legal limit in many places for a business.
- Rules of thumb: flammables in a rated cabinet (not above 10 liters open in the room), acids and bases apart, oxidizers away from fuels, oxygen cylinders at least 6 m (or a 1.5 m wall) from fuel gas.
- Keep stocks low and dated; throw out old or unlabeled containers by the proper route.
Compressed gas cylinders
A cylinder holds gas at up to 200 bar (about 3 000 psi). Two things make that dangerous: the stored energy, which is released all at once if the cylinder fails, and the gas itself (oxygen feeds fires; acetylene, propane and hydrogen burn; argon and CO₂ smother).
Worked example: a 50 liter cylinder at 200 bar
- The cylinder holds 50 L × 197 = about 10 m³ of gas at atmospheric pressure.
- The energy stored by the compressed gas is about p V ln(p ÷ p0) = 200 bar × 50 L × ln(197) = 5.3 MJ, equivalent to 1.3 kg of TNT.
- If the valve is knocked off, gas escaping through a 5 mm opening at 200 bar gives a thrust of about p A = 393 N: on a 70 kg cylinder (weight 687 N) that is an acceleration of 5.6 m/s² sideways, and the cylinder becomes a rocket. Always secure cylinders upright with a chain or strap, and fit the valve cap when not in use.
- Move cylinders on a trolley, with the cap on; never roll or drag them by the valve.
- Store upright and secured, away from heat, in a ventilated place; oxygen separate from fuel gases.
- Open valves slowly, stand to the side of the regulator, and never use oil or grease on oxygen fittings (they can ignite).
- Use the right regulator and hose for each gas, check for leaks with soapy water, and fit flashback arrestors on oxy-fuel sets.
- Acetylene must not be used above 15 psi (1.0 bar) because it becomes unstable; its flammable range is very wide (2.5 to 81 % in air).
- Check dates and condition: a cylinder out of test or dented should be returned to the supplier.
Oxygen, nitrogen, argon and CO₂ in a room
Air is 20.9 % oxygen. Gases that are not themselves toxic (nitrogen, argon, helium, CO₂ in large quantity) kill by displacing the oxygen, without warning: you do not feel short of breath. The reverse hazard, oxygen enrichment, makes everything burn. Both are calculated from how much gas leaks and the room volume: for a well-mixed room the fraction after adding a volume Vadd of gas is c = 1 − (1 − c0) e−Vadd ÷ V for oxygen and c = c0 e−Vadd ÷ V for an inert gas.
| Oxygen in the air | Effect |
|---|---|
| 20.9 % | Normal air |
| 19.5 % | Minimum safe level (oxygen-deficient below) |
| 16 % | Judgment and coordination impaired |
| 12 % | Dizziness, faster breathing, poor judgment |
| 10 % | Nausea, vomiting; may collapse without warning |
| below 6 % | Unconsciousness in seconds, death in minutes |
Worked example: leaks in a shop
- Oxygen leak: 10 m³ (a full cylinder) into a 50 m³ room gives 35.2 % oxygen, far above the 23.5 % at which clothes and materials burn fiercely. Into a 10 m³ store it would be 71 %. Never use oxygen to “freshen” a room or blow dust off clothes.
- Argon leak: 10 m³ into 50 m³ leaves 17.1 % oxygen (below the 19.5 % safe level); a smaller 3 m³ leak leaves 19.7 %. In a 10 m³ booth, 10 m³ of argon leaves only 7.7 %: unconsciousness in seconds. Argon is heavier than air and pools in pits and low corners.
- Dry ice: 1 kg of dry ice makes 0.56 m³ of CO₂ gas: 5.6 % in a 10 m³ closed car or small room (headache, breathing difficulty above 3 to 5 %), 1.1 % in the 50 m³ shop. Carry and store it in a ventilated place.
- Confined spaces (tanks, pits, booths) need testing and a standby person; never go in after a collapsed person without breathing apparatus.
Welding and cutting
Welding combines almost every hazard: arc light, fume, heat, spatter, electricity, gas and fire. The earlier pages cover each (Dust, Fumes and Ventilation, Fire, Fuels and Explosion, Electrical Safety); here are the points specific to the process.
| Arc current | Minimum lens shade (stick) | Typical shade (MIG/TIG) |
|---|---|---|
| Up to 60 A | 7 | 8 |
| 60 to 160 A | 8 | 10 |
| 160 to 250 A | 10 | 12 |
| 250 to 550 A | 11 | 14 |
Worked example: arc eye
- The arc’s ultraviolet burns the cornea in minutes without any sensation at the time: a few seconds of an unshielded arc at 1 m can cause “arc eye”, which shows as a sandy, painful feeling 6 to 12 hours later.
- The dose falls with the square of the distance: at 3 m it is 9 times less, but still enough for a bystander looking at the arc. Screen the area with welding curtains and tell people not to look.
- Use the helmet before you strike the arc; check the lens for cracks and the correct shade, and replace the cover lens when it is spattered.
- Skin burns from UV also occur under thin clothes: cover all skin with flame-resistant clothing and leather gloves.
- Remove coatings and check the metal: galvanized, painted, plated, stainless and cadmium-plated parts give toxic fumes (see Dust, Fumes and Ventilation).
- Never weld on a container that held fuel or solvent, even after it has been emptied.
- Chlorinated solvents (degreasers) near an arc form phosgene: keep them away.
- Keep the earth clamp near the work, not through bearings or chains, and the cables in good order (see Electrical Safety).
- Oxy-fuel: light the fuel first, set the flame, check regulators and flashback arrestors, and turn the gas off at the cylinder when you finish.
- Fire watch after hot work (see Fire, Fuels and Explosion).
Spills, burns and eye splash
Worked example: how much water for a splash
- An eyewash station delivers at least 1.5 L/min for 15 minutes: 22.5 liters. A bottle of saline from a first-aid kit is only a start. Flush for the full 15 minutes with the eyelids held open.
- A safety shower delivers about 75.7 L/min: 1 136 liters over 15 minutes. A hose or a tap is a poor second best but is better than waiting.
- Speed matters more than the source: acid or alkali does most of its damage in the first minute.
- Skin: remove contaminated clothing and flush with water for 15 to 20 minutes; do not neutralize; seek medical advice.
- Swallowed or inhaled: call the poison center or emergency number with the SDS to hand; do not induce vomiting unless told to.
- Small spills: ventilate, remove ignition sources, absorb with a non-combustible absorbent, put in a sealed container and dispose of it properly.
- Large spills or unknown chemicals: leave, close the door and call for help.
- Keep spill materials (absorbent, gloves, bags) where the chemicals are stored.
Waste and disposal
- Never pour solvents, oils, paint or acids down the drain, onto the ground or into the bin: use the local hazardous-waste collection.
- Keep waste in labeled, closed containers, separated by type (solvents, oils, acids, paint).
- Oily and finish-soaked rags follow the fire page: dry flat or keep wet in a sealed metal can (see Fire, Fuels and Explosion).
- Empty aerosol cans, batteries and fluorescent tubes go to the recycling point, not the household bin.
- Resin and cured plastics from 3D printers have their own rules (see Lasers, 3D Printers, CNC and Soldering).
Troubleshooting
| Problem | Likely cause | Try |
|---|---|---|
| Headache, dizziness, nausea at work | Solvent vapor or poor ventilation | Get to fresh air; stop; improve extraction; switch product |
| Skin rash after epoxy or resin | Sensitization | Stop contact; wash; see a doctor; use better gloves |
| Smell of gas near a cylinder | Leak | Close the valve if safe; ventilate; remove ignition sources; test with soapy water |
| Gritty, painful eyes after welding | Arc eye | Cool compress; no rubbing; see a doctor; use a helmet |
| Unlabeled bottle | Decanted without a label | Treat as hazardous; do not use; dispose by hazardous waste route |
| Cylinder rusty or dented | Damage | Return to the supplier; do not use |
Related
- Workshop Safety: the overview of this guide.
- Fire, Fuels and Explosion: flammable liquids, gas and hot work.
- Dust, Fumes and Ventilation: fumes and ventilation.
- Drilling, Tapping and Fasteners (adhesives) and 3D Printing (resin handling).
FAQ
What is a safety data sheet?
A 16-section document from the maker of a chemical product, giving its hazards, protective equipment, first aid, fire-fighting, storage and disposal. Get one for every product you use.
Is it safe to store a gas cylinder in the shop?
Yes if it is upright, chained, capped, away from heat and (for oxygen) separated from fuel gases; the stored energy is large and a knocked-off valve turns it into a rocket.
Why is argon dangerous in a small room?
It displaces oxygen without any warning smell or sensation: 10 m³ in a 10 m³ room leaves about 8 % oxygen, enough to cause unconsciousness in seconds.
What do I do if I get a chemical in my eye?
Flush with water at once for 15 minutes with the lid held open, remove contact lenses, and get medical help.
References
- OSHA 29 CFR 1910.1200 (hazard communication) and the UN Globally Harmonized System (GHS); CLP Regulation (EC) 1272/2008.
- CGA P-1, Safe Handling of Compressed Gases in Containers; ANSI Z49.1, Safety in Welding, Cutting and Allied Processes; ANSI Z358.1 (emergency eyewash and shower equipment).
- NIOSH, Pocket Guide to Chemical Hazards (exposure limits).
Last reviewed: October 2026. Limits and quantities are illustrative: use the SDS of your own products and the rules that apply to you.