Hot works safety: blowtorch, heat mats and fire watch

Hot work such as soldering, grinding or using a hot-air tool can ignite nearby material during the task or leave smouldering that develops later. Assess the work and consider a method without flame, heat or sparks. Where hot work remains necessary, follow the site’s controls and permit arrangements.

1. Plan and permit. On many sites hot works need a permit that records the precautions and the time limits, so check whether one is required before you start.
2. Clear the area. Remove combustible materials from around the work, or where they cannot be moved, cover and protect them with suitable fire-resistant material.
3. Mind hidden voids. Be alert to what is behind the surface you are heating, because heat can travel through pipes and into wall and floor voids and ignite dust or timber out of sight.
4. Protect with a heat mat. Use a heat-resistant mat or guard between the flame and any surface that could scorch or catch.
5. Prepare for a fire. Keep suitable extinguishing equipment available and know the alarm and escape arrangements. Only a trained person should attempt to tackle a small fire when it is safe and the site plan permits; withdraw if it cannot safely be controlled.
6. Use the minimum heat. Use the right tool and no more heat than the job needs, and never leave a lit torch unattended.
7. Plan the watch before starting. HSE construction guidance calls for a continuous fire watch for at least one hour after hot work stops, with another check two hours after completion, and advises finishing hot work two hours before the end of the working day so the checks can be made. Inspect affected adjacent areas and concealed spaces as well as the joint itself. Higher risks may need longer monitoring; follow the assessment and permit conditions.

Heat can affect areas you cannot see from the joint. A completed solder connection does not end the fire precautions: arrange the watch, later checks and handover before the task begins. Any temporary change to fire detection must be authorised and managed under the site’s fire arrangements, with protection restored as required by that plan.

Storing and handling LPG cylinders

The usual propane blowlamp cylinder supplies vapour and must be kept upright, secured against falling. Laying it on its side can allow liquid LPG to reach the outlet or relief arrangements, producing a much larger volume of flammable vapour if it escapes. Use the cylinder and appliance only the way up they are made to be used; this applies to the vapour-supply cylinders used with a torch.

Store and use them in a well-ventilated area, clear of drains (the gas is heavier than air and can collect in them) and away from heat and other ignition sources. Do not store or use them in an unventilated cabin or other enclosed space, where a leak can build up into an explosive atmosphere.

Oxy-acetylene brazing

Brazing with oxygen and acetylene adds hazards of its own. HSE's leaflets on acetylene and on oxygen give these precautions:

• Flashback arresters go on the pressure regulators of both cylinders, acetylene and oxygen. With long hoses, fit them at the blowpipe as well, and shorten the hose once the long length is no longer needed. Non-return valves on the torch stop gas feeding back into the hoses, but they cannot stop a flashback once it has started.
• Before lighting, purge each hose in turn for a few seconds to clear any mixture of gases, then light the blowpipe with a spark igniter, somewhere well ventilated. For most work the acetylene pressure must not go above 0.62 bar.
• If the blowpipe flashes back, close both of its valves at once, oxygen first and then acetylene, the reverse of the normal order, then close both cylinder valves. If the flame cannot be put out straight away, get everyone clear and call the fire and rescue service. Do not move or vent the cylinder: watch it for heat, and if it gets hot or starts to vibrate, evacuate and call the fire and rescue service.
• Keep acetylene cylinders upright, and never drop, jar or roll them. One that has been lying down is stood upright and left for an hour to settle. Carry them in an open vehicle where you can; a closed van needs ventilation in its load space, because even a small leak can build up an explosive atmosphere.
• Never use oxygen to freshen or cool the air, or to dust down benches or clothing. Air is about 21% oxygen, and a rise to just 24% makes a fire easier to start, hotter and fiercer: clothing and hair can then catch fire easily, and nobody can see or smell the extra oxygen. Take off clothing that may have soaked up oxygen and air it outside. Gas cylinders stay out of confined spaces: feed the gas in by hose instead.
• Keep oil and grease away from oxygen equipment: they can react violently with pure oxygen at high pressure. Check for leaks with a spray or liquid certified for oxygen, never soap, which may contain grease. Open cylinder valves slowly, and close them whenever work stops.

Choosing an extinguisher

Portable extinguishers have red bodies, with a coloured panel that shows what is inside. Use the one that suits what is burning:

• Water (all red): solids such as wood, paper and fabric. It cools the fire, but it is not for burning liquids or anything electrical.
• Foam (cream): solids and burning liquids; it forms a film over a burning liquid. Not for fires involving electricity.
• Carbon dioxide (black): electrical equipment and burning liquids. It leaves no residue, but it does not cool, so it is not suited to burning solids, which can flare up again once the gas has gone. Never hold its horn while it discharges: the horn gets extremely cold and can burn or freeze the skin. Use it only where there is good ventilation, as the gas lowers the oxygen level, and ventilate the area afterwards.
• Dry powder (blue): a multi-purpose type for solids, liquids and gases. In a confined space the powder cloud can take away visibility and make breathing harder.
• Wet chemical (yellow): cooking oil and fat fires only.

Keep extinguishers where people can see them on the way out, near exits and on escape routes, and never where a fire could block the way to them.

First aid for a burn

Treat a burn or scald at once. NHS advice is to hold it under cool running water for 20 minutes, as soon as possible and within 3 hours; cool bottled water or a wet towel will do if there is no tap. Remove clothing or jewellery near the burn, but not anything stuck to it. When it has cooled, lay cling film over it rather than wrapping it round. Do not put creams, oils or butter on it, cover it with a plaster or sticky dressing, or burst blisters. A large or deep burn, a burn to the face, or one caused by electricity or chemicals needs 999 or A&E.