Welding, metalwork, automotive and construction technology

Metal, automotive and construction technology shops prepare students for skilled trades that are in high demand, and they bring a set of hazards that wood shops do not: welding arcs and fumes, hot metal, compressed gases, vehicles on lifts, batteries, fuels and the tools of the construction site. Tom Brennan runs the metal and automotive shops at Pinecrest High School, and Greg Mahler's construction technology class builds a small shed each year in the yard behind the school. This lesson follows their work.

Welding and cutting: the hazards

Welding and cutting are among the most valuable skills a technology program teaches and among the most hazardous. The main hazards are:

• Radiation from the arc. Arc welding produces intense ultraviolet and infrared light. A few seconds of unprotected exposure can cause arc eye, a painful burn of the cornea that feels like sand in the eye a few hours later, and the light can burn exposed skin like severe sunburn. People nearby are exposed too, not just the welder.
• Fumes and gases. Welding produces a fume of tiny metal oxide particles and gases, which vary with the metal, the coating, the rod or wire and the process. Welding fume is classified as a carcinogen by the International Agency for Research on Cancer. Welding galvanized steel releases zinc oxide fume that can cause metal fume fever, a flu-like illness, and welding stainless steel releases chromium compounds that are particularly harmful.
• Burns and fires. Sparks and spatter travel several meters and can ignite clothing, rags, sawdust and anything combustible nearby. Freshly welded metal looks the same hot or cold.
• Electric shock, especially when working in damp conditions or with damaged cables.
• Compressed gas cylinders for oxy-fuel cutting and shielding gas, which can become missiles if a valve is knocked off, and fuel gases that can leak and explode.

Welding and cutting: the controls

School welding areas are usually arranged as individual booths, each with walls or curtains that block arc light from others, local exhaust ventilation, a non-combustible floor and work surface, and a fire extinguisher nearby.

• Ventilation: a fume extraction hood or arm positioned close to the arc captures fume before it reaches the welder's breathing zone. General ventilation alone is not enough for regular welding. Galvanized and coated metals should be avoided in school projects, or the coating removed before welding with suitable controls.
• Eye and face protection: a welding helmet with a filter lens of the correct shade for the process and current, and safety glasses underneath. Auto-darkening helmets are common in schools and must be checked to make sure they switch properly. Booth curtains protect others nearby.
• Clothing: flame-resistant jackets or sleeves, leather gloves, leather boots and no synthetic clothing, which can melt onto the skin. Pockets and cuffs that catch sparks should be closed or avoided.
• Fire prevention: no combustibles within the area sparks can reach, a fire watch after cutting, and never welding on drums or containers that held flammable materials.
• Cylinders: chained upright, capped when not in use, separated by type, moved with a cart, and with regulators and hoses inspected before use.

OSHA's welding, cutting and brazing standards (29 CFR 1910 Subpart Q), enforced by MNOSHA, together with ANSI Z49.1, the American standard on safety in welding and cutting, are the usual references for school welding shops.

Tom introduces welding in stages. Students first learn about the hazards and the protective equipment, then watch demonstrations, then practice on scrap with the teacher beside them. He does not allow students to weld galvanized metal at all, and stainless steel only in senior classes with the extraction arm checked and positioned before each weld.

Grinding and metal machining

Bench grinders, angle grinders, metal lathes and milling machines are common in metal shops. Grinders throw sparks and fragments, and a cracked or wrongly mounted wheel can shatter. On a bench grinder, the tool rest should be adjusted close to the wheel, with a gap of about 3 mm (1/8 in), and the tongue guard at the top close to the wheel as well, so a workpiece cannot be pulled in. New wheels should be checked for cracks and rated for at least the machine's speed. Students should stand to the side when starting a grinder, wear a face shield over safety glasses, and never use the side of a wheel not designed for it.

Angle grinders are among the most dangerous hand tools in any shop, because they spin very fast, can kick back and are easy to misuse. In many school shops they are used only by the teacher or by senior students under direct supervision, with the guard always in place and the side handle fitted. Metal lathes share the entanglement hazards of wood lathes, plus sharp, hot swarf (chips) that should be cleared with a brush or hook, never by hand. The chuck key must never be left in the chuck; many shops use spring-loaded keys that fall out if released.

The automotive shop

Automotive programs work on real vehicles, which bring heavy loads, fuels, batteries, hot fluids and exhaust gases into the classroom.

• Lifts and jacks. A vehicle on a lift or jack can fall and crush anyone underneath. Vehicles must be raised only at the manufacturer's lifting points, lift arms must be positioned and locked, lifts must be inspected regularly, and nobody works under a vehicle supported only by a jack; jack stands rated for the load are always used. Only trained students operate the lift, with the teacher's permission each time.
• Exhaust gases. Running engines produce carbon monoxide, a colorless, odorless gas that can kill. Engines run indoors only with an exhaust extraction hose connected to the tailpipe, and the shop should have a carbon monoxide detector.
• Fuels. Gasoline is highly flammable and its vapor travels along the floor to ignition sources. Fuel is drained only into approved containers, spills are cleaned immediately, and nobody smokes or creates sparks nearby.
• Batteries. Lead-acid batteries contain sulfuric acid and give off hydrogen when charging, which can explode if sparked. Batteries are charged in a ventilated area, and connections are made and broken with the charger off. Hybrid and electric vehicles add high-voltage systems that can cause fatal shocks, and work on them requires specific training and procedures that many school programs restrict to the teacher.
• Fluids and parts. Used oil, coolant, brake fluid and solvents are hazardous and must be collected for recycling or disposal. Brake dust on older vehicles may contain asbestos, so brakes are cleaned with wet methods or a dedicated brake washer, never blown out with compressed air.
• Compressed air and tires. Compressed air can drive particles into the eyes or skin, and over-inflated or damaged tires can burst; tires are inflated in a cage or with a clip-on chuck and remote gauge.

Construction technology

Construction technology programs teach framing, roofing, concrete, drywall, electrical and plumbing basics, often by building a real structure. Greg's class builds a garden shed each spring in a fenced area behind Pinecrest High School. The work brings construction site hazards into the school: falls from ladders and roofs, nail guns, power saws used outdoors, lifting heavy materials, and weather.

• Falls. Students work from the ground, platforms with guardrails, or low scaffolds wherever possible. Roof work on the shed is done at low height with guardrails or from scaffolding, and ladders are set up at the correct angle and tied off. Construction safety law sets fall protection requirements at defined heights, and school projects should be designed so students rarely need to work above the lowest of them.
• Nail guns. Pneumatic and cordless nailers cause many serious construction injuries. Nailers with a sequential trigger, which fire only when the nose is pressed and then the trigger pulled, are much safer than contact-trip nailers and should be used in schools. Students are trained and signed off, keep hands away from the nose, and never point a nailer at anyone.
• Electrical. Outdoor power tools are plugged into GFCI-protected outlets, and cords are inspected for damage.
• Site conditions. The work area is fenced and kept tidy, with materials stacked securely, and work stops in lightning or high winds.

Planning the high-risk tasks

Tom and Greg use a simple risk score to decide which tasks need extra supervision. The program below ranks a few tasks by likelihood and severity on a five-point scale, the same approach used in HSE-360.

# Rank shop tasks by risk = likelihood x severity (1-5 each) and set the supervision level.
tasks = [
    ("MIG welding mild steel in booth", 2, 4),
    ("using angle grinder", 3, 5),
    ("raising car on two-post lift", 2, 5),
    ("charging lead-acid battery", 2, 4),
    ("framing shed wall with sequential nailer", 3, 4),
    ("cutting shingles on the roof", 3, 4),
    ("sweeping the metal shop", 2, 2),
]
def level(score):
    return "teacher only or 1:1 direct supervision" if score >= 15 else ("close supervision, signed-off students" if score >= 8 else "normal supervision")
for name, lik, sev in sorted(tasks, key=lambda t: -t[1] * t[2]):
    print(f"{name:42} {lik*sev:2d}  {level(lik*sev)}")

using angle grinder                        15  teacher only or 1:1 direct supervision
framing shed wall with sequential nailer   12  close supervision, signed-off students
cutting shingles on the roof               12  close supervision, signed-off students
raising car on two-post lift               10  close supervision, signed-off students
MIG welding mild steel in booth             8  close supervision, signed-off students
charging lead-acid battery                  8  close supervision, signed-off students
sweeping the metal shop                     4  normal supervision

The angle grinder rises to the top and is restricted to the teacher or one-to-one supervision. Lift work, welding and roof work need close supervision of signed-off students, and cutting on the roof is a candidate for redesign: cutting shingles on the ground and passing them up removes the need for a power tool at height.

Clothing and protective equipment in metal and auto shops

Protective equipment in these shops is task-specific. Safety glasses with side shields are worn throughout, with a face shield added for grinding and chipping slag. Safety footwear protects against dropped parts and hot metal. Gloves are chosen for the job: leather for welding and handling hot or sharp metal, chemical-resistant gloves for fuels and solvents, and no gloves at all on rotating machines such as lathes and drill presses. Students should not wear synthetic fleece or nylon in the welding area, because it melts and sticks to the skin if a spark lands on it; cotton or wool clothing under a flame-resistant jacket is much safer.