Falling objects, other trades and an incident investigation

By late June the steel at the Prairie Gate Community Centre was topped out, the tilt-up walls were connected to the gymnasium roof, and the library's CLT roof was on. The building was full of other trades: electricians pulling wire, plumbers hanging pipe, sheet metal workers running ductwork, curtain wall installers on the outside of the classroom wing and concrete crews placing the composite floor slabs. Every one of them worked under or beside the ironworkers who were still finishing connections, welding studs and installing the last braces. This final lesson covers protection from falling objects, working alongside other trades, and how Tallgrass investigated the one serious incident on the job, using everything the earlier lessons covered.

Why falling objects are so dangerous

A small object dropped from height carries a surprising amount of energy. A 2.3 kg (5 lb) spud wrench dropped 9 m (30 ft) hits the ground at about 13 m/s (44 ft/s) with roughly 200 joules of energy, enough to cause a serious head injury even through a hard hat, and far more if it lands point first. Bolts, nuts, drift pins, offcuts and welding rod stubs are smaller but fall in large numbers. A dropped piece of deck or a beam that slides off a stack can kill instantly.

# Impact energy of dropped objects (energy = m * g * h; air resistance ignored).
import math
g = 9.81
items = [("hex nut", 0.05), ("structural bolt and nut", 0.4), ("drift pin", 1.0),
         ("spud wrench", 2.3), ("impact wrench", 9.0)]
for h in (4.0, 9.0):
    v = math.sqrt(2 * g * h)
    print(f"dropped {h:.0f} m: impact speed {v:.1f} m/s")
    for name, kg in items:
        print(f"   {name:24} {kg * g * h:7.0f} J")

dropped 4 m: impact speed 8.9 m/s
   hex nut                        2 J
   structural bolt and nut       16 J
   drift pin                     39 J
   spud wrench                   90 J
   impact wrench                353 J
dropped 9 m: impact speed 13.3 m/s
   hex nut                        4 J
   structural bolt and nut       35 J
   drift pin                     88 J
   spud wrench                  203 J
   impact wrench                795 J

Controls for falling objects

Falling object protection works best in layers, starting with keeping objects from falling at all. Under the general duties in Manitoba's regulation, the employer must protect workers from falling objects, and Tallgrass's erection plan at the Prairie Gate Community Centre set out the layers it used.

• Keep it from falling. Tools tethered to the worker or the structure, using tethers and attachment points rated for the tool's weight; bolt bags and buckets with closures; loose material secured at the end of each task; bundles secured on the frame; no throwing of tools or material.
• Catch it if it falls. Toe boards and debris netting on perimeter cables and platforms; debris nets under work areas; covers over openings and gaps.
• Keep people out from under it. Barricaded exclusion zones below active steel work and hoisting routes; scheduling other trades so they do not work directly below the ironworkers; covered walkways where people must pass under the work.
• Protect the head. Hard hats, with chin straps when working at height or looking up, as the last layer.

Tool tethering has its own standard, ANSI/ISEA 121, which sets requirements for tethers, attachment points and containers used to prevent dropped objects. At the Prairie Gate Community Centre, every tool used above the first floor had to be tethered with equipment rated for its weight, and the tethers were inspected like other personal equipment.

Working with other trades

As the building filled with trades, coordination became as important as any piece of equipment. Each morning at the Prairie Gate Community Centre, Rosa Delgado held a 15-minute coordination meeting with the foremen of every trade on site. They reviewed where the ironworkers would be working and hoisting that day, which floors and areas were closed below them, which perimeter cables or covers would be removed or changed, and who needed the crane. A large board in the trailer showed each floor and the trade working in each area.

• No work below active steel erection or hoisting unless overhead protection was provided, as the plan required.
• Fall protection handover. Trades used perimeter cables and covers only on floors Tallgrass had accepted from the erector, as lesson 9 described.
• Nobody touches temporary bracing except the erector, as lesson 7 described.
• Permits. Hot work, removal of covers or cables, and crane use by other trades all needed permits from Tallgrass.
• Shared equipment. Lifts and scaffolds used by more than one trade were inspected by each user before use.

Other trades often have less experience at height than ironworkers. A sheet metal worker installing duct hangers from a ladder near the slab edge, or an electrician walking a beam to reach a junction box, may not know the hazards of an incomplete frame. Tallgrass's orientation for every new worker included a section on the frame: where the edges were, which areas were closed, and what not to touch.

The incident

On 3 July, at about 10:40 in the morning, a deck bundle tipped on the gymnasium roof. Kyle Bear's decking crew was landing the last roof deck bundles. One bundle, about 1.8 t (2 tons), was landed across three joists near the east wall. As the crew prepared to unband it, the bundle rolled toward the open side of the roof, two joists twisted sideways, and the bundle and about a dozen sheets fell to the floor of the gymnasium 9 m (30 ft) below. A decker, Ellie Ross, was knocked off her feet by the moving sheets and fell over the leading edge. Her SRL, attached to the overhead horizontal lifeline, arrested her after about 1 m (3 ft). She was rescued with the boom lift within eight minutes and taken to hospital with a broken wrist and bruising. The floor below had been barricaded, and nobody was under the bundle.

The investigation

Tallgrass investigated with a team that included Owen Hartley, Bill Okafor, Kyle Bear, a worker member of the workplace safety and health committee, Sanjay Mehta and the joist supplier's engineer. They used a causal factor approach: they built a timeline, identified each event or condition that, if removed, would have prevented the incident or reduced its severity, and for each one asked why it happened until they reached causes the organization could fix.

Tallgrass reported the incident as the regulation requires, since it involved a structural failure and a worker taken to hospital, and preserved the scene until the investigation team and the Branch's safety and health officer had seen it. The officer reviewed the erection plan, the bridging records and the training records and accepted the corrective action plan.

Corrective actions

The team chose corrective actions starting at the top of the hierarchy of controls, not with retraining alone.

• Engineering. A hold point was added to the erection plan: no bundle may be landed on joists until Bill or Kyle confirms in writing, on a bay-by-bay checklist, that all bridging is installed and anchored and joist bearing ends are attached. Landing locations were marked on the steel with paint before each bundle went up.
• Coordination. All roofing and other material deliveries to the roof had to be scheduled through Rosa's coordination meeting and could not be landed on an area until decking there was complete.
• Procedure. When unbanding near an edge, the crew stands on the side of the bundle away from the edge, and the bundle is checked for stability by two people before the bands are cut.
• Training. The decking crew and the bridging crew walked through the new hold point and procedure on site.
• Sharing. Tallgrass shared a summary with the other employers on site and with Northern Iron Erectors Ltd.'s other projects.

# Simple tracker for corrective actions (invented status at two weeks).
actions = [
    ("Bridging hold point added to erection plan", "engineering", True),
    ("Landing spots painted on steel before lifts", "engineering", True),
    ("Roof deliveries via coordination meeting", "coordination", True),
    ("Unbanding stance procedure", "procedure", True),
    ("Crew walkthrough of new procedure", "training", True),
    ("Summary shared with other employers", "sharing", False),
]
done = sum(1 for _, _, ok in actions if ok)
print(f"{done} of {len(actions)} actions complete")
for name, kind, ok in actions:
    print(("done   " if ok else "OPEN   ") + f"{kind:12} {name}")

5 of 6 actions complete
done   engineering  Bridging hold point added to erection plan
done   engineering  Landing spots painted on steel before lifts
done   coordination Roof deliveries via coordination meeting
done   procedure    Unbanding stance procedure
done   training     Crew walkthrough of new procedure
OPEN   sharing      Summary shared with other employers

What the incident shows

The incident pulled together almost every topic in this course. Site layout and delivery planning (lesson 3) put insulation where the bundle should have gone. The erection plan (lesson 2) had assumed complete bridging without a hold point to confirm it. Structural stability (lesson 7) failed locally because joists without bridging could roll. Landing bundles (lesson 8) went wrong because the landing spot changed on the fly. And the protection that worked, the overhead SRL and engineered lifeline (lesson 9), the rescue plan and the barricaded area below (lesson 12), turned what could have been a fatality into a broken wrist.

Course review: questions before any erection work

Before any crew starts erection work on a Tallgrass site, the foreman should be able to answer these questions:

• Is there a current, reviewed site-specific erection plan, and has the crew been walked through it?
• Have the foundations, anchor rods and any repairs been confirmed in writing?
• Can the crane make every pick from a pad checked for buried services and bearing capacity?
• Is the rigging inspected and right for each load, and is everyone clear of the load path?
• Does every member get the required bolts before release, and is the frame braced at the end of each shift?
• Is everyone at height protected, with enough clearance, and is there a rescue plan with equipment on site?
• Are tools tethered, areas below barricaded and other trades kept clear?
• Is hot work under permit with a fire watch?