Lesson 27 makes the student walk the layout as the person who works and services the system, and turns that walk into a guarding audit. The one thing every student must leave with: safety is a scoping discipline, and underside guarding is decided by exposure, never by a fixed height. This lesson also carries three binding fact-check corrections that override the old Module 10 slides. Read the correction note before you teach, so you don't repeat a myth from memory.
The old Module 10 and the old instructor guide taught three things that are wrong and are corrected in this lesson. Do not repeat them from memory or from the old slides.
| Segment | Min | What happens |
|---|---|---|
| Hook: act like the person | 8 | Open cold on the flagship walk. Earlier they acted like the carton; now they act like the person who uses and fixes the system. Read the operator's-eye questions aloud and land the frame: safety is a scoping discipline, and the lab's output is the guarding audit. Ask who has cleared a jam alone at 2 AM. |
| Categories + the underside rule | 12 | Walk the five guarding categories, then teach the corrected underside rule straight: guard by exposure, not by a number. Run the staircase case. When a student reaches for "it's above some height so it's exempt," stop and run the exposure test instead. |
| Pull cords: mandate vs field practice | 10 | Separate the codified mandates (slack-cable switch, full accessible length, 5 ft reach, 25 ft access, 50 ft bulk) from field practice (the 30-48 in / 10-12 ft numbers). Then the E-stop-zone and master-safety-system logic. Name that the cord stops the full zone; the safety-PLC circuit is Lesson 20's. |
| Caging, robot type, interlocks | 12 | Teach the risk-assessed collaborative-application model, not the cobot label. Ask the integrator for the risk assessment document. Then the interlock point: a safety gate needs a safety-rated device, and a standard limit switch isn't equivalent. Push on where students would put the wrong switch. |
| LOTO, access, ergonomics, the map | 10 | LOTO reachable by one person from the floor, no ladder, no second person, multi-lock hasps in scope early. Maintenance safe-access as the other half of Lesson 26's wrench question. Then the regulatory map: ASME B20.1-2024 primary, general-industry vs construction, NFPA 70 supporting. |
| Riverside audit + Forest close | 8 | Run the guarding audit on the Riverside layout: pull cords over 300 ft, the forklift crossing and its two near misses, the underside exposure on the decline and the stairway, bearing guards, and LOTO for a team of one. Close on: safety found in scoping costs nothing. |
| Total | 60 | Baseline session. Expand with the stretch option below for a 90-minute block. |
Give the room a mezzanine layout with conveyor overhead and workers below, and have them find every safety requirement. Most will find the obvious ones. Push them to the underside exposure, the pull-cord path, and the bearing guards on the mezzanine drive shafts, the ones they'd miss on a real project.
The pivot is the underside. When a student reaches for "it's above 96 inches so it's exempt," stop them on the spot and run the exposure test and the staircase case instead. That single correction is what this lesson turns on: exposure decides the guard, not a floor-measured height. Don't let the old rule survive the room.
Every one of these is the old training or the shortcut talking. Correct each on the spot.
Run the guarding audit on the Riverside layout as the session's spine. Instructor-note pattern: don't tell them, ask. Grade the reasoning, especially whether they judged the underside by exposure rather than by a floor number.
Three beats to push. The forklift crossing: let the two near misses set the urgency, and make them name the guarding and signaling the crossing needs. The underside on the mezzanine decline: exposure, not a 96-inch measurement, and the stairway up to the mezzanine is its own exposure point. LOTO for a team of one: every isolation point reachable by Michael alone, from the floor, no ladder, no second person. Don't let anyone leave the beat with the audit still a slogan instead of priced lines.
Question 1 (underside by exposure). The student evaluates exposure: whether anyone can be under or near the discharge and reach path of the run, judged against ASME B20.1, which requires spill or pan guards wherever falling material or a reach-in could endanger someone below, regardless of mounting height. A floor-measured height isn't the answer because there's no universal height that exempts underside guarding, and the staircase proves it, a person on the stairs can reach a run that measured plenty high from the floor. Strong answers name the exposure test, refuse to give a fixed number as the rule, and use the staircase to show why the floor measurement misleads. Weak answers reach for "96 inches" or any clearance figure as an exemption.
Question 2 (robot cell + interlock). Before deciding the cell runs without full perimeter guarding, the student needs a documented risk assessment showing the application meets a recognized collaborative-application technique (power-and-force-limiting, speed-and-separation-monitoring, hand-guiding, or safety-rated monitored stop) under ISO 10218-1:2025 and ISO 10218-2:2025. The "collaborative" marketing label isn't enough; safety is a property of the application, and a robot running at full speed reaching outside a fixed footprint is unlikely to qualify without that document. Separately, a gate interlock is a safety device only when it's a safety-rated device; a standard limit switch isn't equivalent. Strong answers separate application from label and name the safety-rated requirement on the gate.
The guarding audit is a project-folder artifact, the same habit the Riverside note has built since Part I. A disciplined student carries this audit straight into the capstone, and it feeds the proposal's safety scope, so every guard, pull cord, cage, and bearing cover is priced in from the start instead of surfacing as a change order. That's the whole payoff of teaching safety as a scoping discipline: the audit becomes money already in the number.
Never announce it. Your job is to make the audit feel like normal engineering, not a trick. The student who kept it will find it waiting when the capstone asks for the safety scope, and the reveal is theirs.