Hot work in special locations

The basic precautions of hot work, avoiding it where possible, removing or protecting combustibles, testing the atmosphere and keeping a fire watch, apply everywhere. Some locations add hazards that need extra controls or different thinking. Roofs hide fire inside their layers. Occupied buildings, hospitals and data centres cannot simply be cleared of people or equipment. Process plants and fuel terminals can release flammable gas at any moment. Confined spaces concentrate fumes and change oxygen levels. Construction sites have little fire protection and lots of fuel. This lesson looks at hot work in each of these settings.

Torch-applied roofing

Torch-applied roofing uses a propane torch to melt the bitumen on the underside of modified bitumen membranes so they bond to the layer below. It is fast and produces durable roofs, but it brings an open flame of over 1,000 °C onto a roof assembly that may include wood decking, cant strips, insulation, old felts and hidden cavities. Fire can start inside the assembly, at flashings, around penetrations and at the edges, and smoulder out of sight for hours before breaking through. Roofing torches have caused some of the largest hot work losses, including fires that destroyed schools, churches and apartment buildings.

Roofing contractor associations have developed specific training for torch-applied roofing. The Canadian Roofing Contractors Association and provincial associations promote torch safety training and practices, and many insurers and owners require certified torch applicators. Key practices include:

• Never torch directly onto a combustible deck, wood blocking, cant strips or exposed insulation; install a noncombustible or mechanically fastened base sheet first.
• Do not torch in torch-free zones: at flashings, around penetrations, at edges and anywhere the flame could enter a gap or cavity. Use self-adhered membranes, cold-applied adhesives or hand-sealed details there.
• Keep the propane cylinder upright, away from the torching area and hatches, and shut it off at the cylinder when work stops.
• Have at least two suitable extinguishers on the roof within reach of the torch operator.
• Keep a fire watch for the required time after torching stops: at least 60 minutes under the National Fire Code, and longer where the insurer or owner requires, often with a final check using a thermal imaging camera.
• Stop torching well before the end of the day so the fire watch and final check happen in daylight with people present.

Many owners now ban torch-applied roofing on occupied, heritage or wood-frame buildings, and specify alternatives such as self-adhered, cold-applied or mechanically fastened membranes, or single-ply membranes welded with hot air, which carry far less fire risk.

Occupied buildings, hospitals and heritage sites

In offices, schools, hospitals, care homes, hotels and apartments, hot work must protect people who may not be able to evacuate quickly and who are not part of the work. Smoke from a small fire can spread through ducts and corridors and harm people far away. Hot work in these buildings is best done when the area is unoccupied, with smoke compartments closed, and with fire alarms in service. Health care facilities often require interim life safety measures when work affects fire protection, and infection control rules may limit dust and smoke.

Heritage buildings, churches and museums need special care. Large concealed roof spaces, old dry timber, decorative linings and irreplaceable contents mean a fire can be catastrophic. Many owners of heritage buildings ban open-flame work entirely, require cold methods, or allow hot work only in temporary noncombustible enclosures with extended fire watches and thermal imaging checks.

Data centres, telecommunications and clean environments

Data centres and telecommunications facilities are designed to keep fire out: very early smoke detection, pre-action or gaseous fire suppression, and strict control of combustibles. Hot work threatens all of these. Smoke and fume can trigger aspirating smoke detectors and release clean agent suppression systems, which are expensive to refill and can disrupt operations. Dust and metal particles can damage servers. The usual approach is to avoid hot work in white space altogether, fabricate off site, and use cold methods such as grooved couplings and mechanical fasteners for pipework and supports.

When hot work cannot be avoided, it is planned with the facility's operations team: detection and suppression zones may be placed in a controlled bypass with a documented impairment, a fire watch with suitable extinguishers stands by, the area is screened and ventilated to keep fume away from equipment, and systems are restored and tested immediately afterward. Similar principles apply in clean rooms, laboratories and control rooms. The data centre safety courses in this stream cover these facilities in more depth.

Process plants, refineries and fuel terminals

In refineries, chemical plants, gas plants, terminals and fuel storage sites, flammable gas can be released at any time from leaks, relief valves, sampling, maintenance on other equipment or upsets elsewhere in the plant. Hot work in operating areas is therefore controlled very tightly, usually under a site-wide permit-to-work system that coordinates hot work with other permits and with operations.

Industry practice in Canada follows the same guidance used internationally, including API Recommended Practice 2009, Safe Welding, Cutting, and Hot Work Practices in the Petroleum and Petrochemical Industries, and API RP 2201 for hot tapping, alongside provincial OHS rules and CSA Z767 for process safety management. Typical controls include continuous gas monitoring with alarms at the work and at nearby drains, covering sewers and drains, checking wind direction, and stopping work instantly when gas is detected or an alarm sounds.

Pressurized welding habitats are temporary enclosures built around the hot work and supplied with clean air from a safe location, keeping the inside at a slightly higher pressure than outside so flammable gas cannot enter. They include gas detectors at the air intake and inside, and they shut off the welding power automatically if gas is detected or the pressure is lost. Habitats allow hot work to continue in operating plants with much less risk, but they must be designed, installed and monitored by trained people.

Hot tapping, welding a fitting onto a pipe or vessel that is in service and then drilling through it, is a specialized form of hot work used to avoid shutting down a process. It requires engineering review of the pipe wall, the contents, flow and pressure, and should be done only by qualified specialists following a written procedure.

Confined spaces

Hot work in a confined space combines two of the most dangerous activities in industry. Fumes and gases concentrate quickly. Oxygen can be depleted by combustion or displaced by shielding gases such as argon and carbon dioxide, or increased by leaking oxygen hoses, making clothing extremely flammable. Flammable gas can enter from connected lines or be released from residue when it is heated. Escape is difficult, and rescue is slow.

Hot work in a confined space needs the full confined space program covered in HSE-211 in addition to the hot work permit: isolation of all lines, cleaning, continuous atmospheric monitoring for oxygen, flammables and toxic gases, forced ventilation with clean air, never using oxygen for ventilation, gas cylinders kept outside the space, torches and hoses removed during breaks, an attendant outside, a fire watch, and a rescue plan. Many sites require continuous monitoring inside the space during hot work and a fire watch both inside and outside where sparks could reach.

Construction and demolition sites

Buildings under construction or demolition are at their most vulnerable to fire. Sprinklers and fire separations may not yet be installed or may be removed, and combustible packaging, formwork, scaffold boards and debris are everywhere. Wood-frame and mass timber buildings under construction have burned down in large fires, some started by hot work. The National Building Code (Part 8) and the National Fire Code (Section 5.6) require fire safety planning at construction and demolition sites, including control of hot work, and many municipalities and insurers require a fire safety plan and a designated fire safety manager for large wood buildings during construction.

Good practice on construction sites includes daily removal of combustible waste, designated hot work and storage areas, charged standpipes and temporary fire protection as the building rises, hot work permits issued by a single site authority, and security patrols after hours.

Ships, vehicles and other unusual places

Hot work on ships, barges, rail tank cars and road tankers combines confined spaces, residues of flammable cargo and limited escape. Marine work in Canada falls under the Canada Labour Code and the Maritime Occupational Health and Safety Regulations, and tanks and holds that carried flammable cargo usually need certification by a competent person that they are safe for hot work. Vehicles bring their own hazards: fuel tanks and lines, upholstery, batteries that release hydrogen, and, for electric vehicles, high-voltage batteries that must never be heated. In every case, the same rule applies: find out what the space or object contains, make it safe and test it before any hot work.