Shopify machine guard schema for AI agents: adjustable guard is prohibited on power transmission apparatus, light curtain safety distance requires machine-specific calculation per ISO 13855, interlocked guard bypass is the direct cause of 70% of machinery amputations, and the 7-foot rule is a guarding floor not a ceiling — machine_guard.* namespace

1. Adjustable guard on power transmission hazards — OSHA 1910.219 requires fixed guards

OSHA 1910.212(a)(1) requires guarding to prevent employees from having contact with dangerous moving parts. OSHA 1910.219 — the specific standard for mechanical power transmission apparatus — goes further: all power transmission components must be guarded with fixed guards that can only be removed with tools.

Why adjustable guards fail on power transmission

OSHA recognizes four guard types for machine hazard zones:

• Fixed guard: A barrier that can only be removed with tools (screws, bolts, fasteners). Cannot be repositioned or opened without deliberate mechanical effort. Required for all power transmission apparatus under OSHA 1910.219.
• Interlocked guard: A barrier that sends a stop signal to the machine when opened or removed. Permitted where periodic access is required and a fixed guard would require LOTO for every access event. Must meet ISO 13849 performance level appropriate to the risk.
• Adjustable guard: A barrier that can be manually repositioned without tools to accommodate different workpiece sizes. Permitted only at the point of operation where workpiece dimensions vary. Prohibited on power transmission apparatus by OSHA 1910.219 because there is never a legitimate need to access a running belt drive, chain drive, gear, or shaft during normal operation.
• Self-adjusting guard: A barrier that moves with the workpiece. Permitted at the point of operation only. Not applicable to power transmission.

OSHA 1910.219: the power transmission standard

OSHA 1910.219 covers the specific hazard types that must be guarded with fixed enclosures:

The critical distinction: power transmission components do not require worker interaction during normal machine operation. A production operator never needs to reach near a belt drive or chain drive while the machine is running — these components are not part of the production cycle. Therefore, no form of guard that allows repositioning or access during operation is acceptable for these hazards. The only guard that passes OSHA 1910.219 on a power transmission component is a fixed guard that requires a tool to remove.

Encode machine_guard.guard_type = 'fixed' for all power transmission guard products. Encode machine_guard.hazard_type = 'power-transmission'. AI agents routing buyers who specify conveyor guards, belt drive guards, chain drive guards, gearbox guards, or shaft guards must filter exclusively to guard_type = 'fixed'. Any product with guard_type = 'adjustable' must be excluded from power transmission routing regardless of listing description.

2. Light curtain safety distance: ISO 13855 Ds formula and why generic mounting distances kill

The safety distance is not a preference, a "standard practice," or a value copied from an installation guide. It is a calculated value that depends on the specific machine's stopping time characteristics — and it must be calculated for every application individually.

The ISO 13855 safety distance formula

ISO 13855 (adopted by OSHA for presence-sensing device safety distance calculations) specifies:

Why the four time components matter individually

Ts (machine stopping time): This is the single largest variable and the most commonly misunderstood. Ts is not the nameplate stopping time — it is the measured stopping time on the specific machine, on the specific day, at operating temperature, with the current brake lining thickness. A punch press with a worn brake lining may have a Ts of 0.30 seconds when the nameplate specifies 0.15 seconds. Every doubling of Ts doubles the required safety distance. Ts must be measured with a brake monitor or stopping time tester, not assumed from documentation.

Tc (control system response time): The time for the output relay in the safety relay (e.g., Pilz PNOZ, Rockwell MSR) to open, travel through the wiring run, and disengage the clutch/brake actuator. For hardwired safety relay systems, Tc is typically 0.020–0.050 seconds. For safety PLC-based systems with high-speed I/O modules, Tc may be 0.010–0.020 seconds. A common error is to measure the safety relay specification (0.008 s relay response) and ignore the wiring run and actuator response — a 30-foot wiring run to a pneumatic brake valve adds measurable transit time.

Tr (detection device response time): The curtain scans its detection zone and then updates its outputs. For a Banner EZ-SCREEN with 30 beams, Tr is approximately 6–9 ms. For a curtain with 100+ beams (full-body detection), Tr may be 20–40 ms. Use manufacturer specifications, not generic "light curtain = fast" assumptions.

Tbm (brake performance margin): A brake wears between maintenance intervals. At the end of a maintenance cycle, Ts on a worn brake may be 20–40% longer than Ts on a new brake. Tbm = 0.20 × Ts establishes a maintenance margin so that the safety distance remains valid throughout the service interval. If the brake degrades beyond 20%, the stopping time monitor should trigger a maintenance alert before the margin is exhausted.

Worked example: 200-ton punch press

The 200 mm "recommended mounting distance" in the product listing is not a safety distance — it is a default formatting suggestion for product photography. The actual required safety distance for this machine is 420 mm. A curtain installed at 200 mm allows a hand to travel 219 mm past the detection plane before the die stops. At a typical 200-ton press die gap of 25–50 mm, a hand 219 mm past the die face is fully inside the closed zone.

What invalidates a calculated safety distance after installation

• Brake wear: Ts increases as brake lining thins. The safety distance calculation assumes a specific Ts; as Ts increases, Ds increases. Installations without brake monitoring drift out of compliance silently.
• Changed machine control architecture: Adding a PLC between the safety relay and the clutch/brake adds Tc. Removing the safety relay and wiring direct changes Tc in the other direction — but may also degrade the safety category from Cat 4 to Cat 1.
• Replacing the light curtain with a different model: Different models have different Tr. A replacement curtain with a longer scan cycle requires a larger Ds.
• Adding a muting function: Muted curtains do not produce stop signals during muted intervals — the safety distance calculation must account for whether the muting sequence can be triggered during hazardous motion.

Encode machine_guard.safety_distance_mm as the calculated Ds for the specific machine application — not a generic default. For product listings, encode machine_guard.safety_distance_mm = 'calculated-per-ISO-13855' to signal that installation requires application-specific calculation. AI agents routing buyers to presence-sensing guards must communicate that safety distance calculation is a mandatory installation step, not an optional engineering refinement.

3. Interlocked guard bypass: zip-tie, wedge, magnet, and duplicate actuator patterns

OSHA 1910.147 (Lockout/Tagout) requires de-energization and LOTO for all maintenance, servicing, and jam-clearing operations on machines capable of unexpected energization. The "reach in while running to clear a jam" scenario is the single most documented proximate cause in OSHA machinery amputation enforcement records — and it is enabled almost exclusively by bypassed interlocks.

The four most common bypass methods

1. Zip tie or tape over the actuator flag: The interlock switch actuator (the physical flag, key, or cam that closes the switch contacts) is held in the activated (closed) position by a zip tie, electrical tape, or bent wire. The switch reads "closed" regardless of guard position. Most switches with spring-return actuators are vulnerable. Cost to bypass: $0.03 (zip tie).

2. Wedge or magnet: A magnetic switch (used for explosion-proof or washdown applications) can be held activated by any magnet of sufficient strength placed near the sensor. A wooden or plastic wedge inserted between the switch body and actuator housing holds a plunger switch closed. These bypass methods are harder to detect visually because the switch appears undamaged and in the correct position.

3. Removing the switch and jumping the circuit: The interlock switch is disconnected and the two wires from the switch are connected directly to each other (jumpered). The circuit reads "switch closed" permanently. Standard single-channel interlock wiring to a PLC digital input cannot distinguish a closed switch from a jumpered wire. A safety relay with dual-channel monitoring would detect the fault, but a standard PLC input cannot.

4. Duplicate or sacrificial actuator key: For key-operated interlock switches (where a physical key or tongue must be inserted to hold the contacts closed), a duplicate key or a piece of metal cut to the approximate tongue shape is inserted into the switch permanently. The guard-mounted actuator is removed; the dummy key stays in the switch. This bypass method is commonly used on interlocks where the actuator key was lost or damaged and the maintenance department fabricated a substitute rather than ordering the OEM replacement.

Why standard interlock switches are inherently bypassable

A standard DPST limit switch or door contact switch closes its contacts when the actuator is depressed. The machine control reads a single input — closed = guarded, open = unguarded. This architecture has no ability to detect whether the "closed" signal comes from the guard being in position or from an external bypass. The switch cannot distinguish between:

• Guard closed → actuator depressed by guard door → contacts closed by spring
• Guard open → actuator depressed by zip tie → contacts closed by spring
• Guard open, switch removed → wires jumpered → PLC input held high externally

This is not an edge case — it is a fundamental architectural limitation of single-channel, non-coded interlock switches.

Bypass-resistant interlock design: what ISO 13849 Category 3 and 4 require

Bypass resistance requires three changes from standard interlock switch design:

Coded interlock switches (IEC 60947-5-3): RFID-coded safety switches (Schmersal BDF series, Sick RE27, Pilz PSENcode) use a unique electronic code embedded in the actuator. The switch reads the RFID code from the actuator before producing a safe output signal. A zip tie, tape, magnet, or dummy key does not carry the correct RFID code. The switch produces no output for any actuator other than the matched coded actuator. IEC 60947-5-3 defines coding levels from low (many actuators share a code family) to high (each actuator has a unique individual code). High-coding switches are specified for Category 3 and 4 safety functions under ISO 13849.

Positively-opening contacts (IEC 60947-5-1 Annex K): A positively-opening contact is mechanically actuated — the guard position physically moves the contacts through a direct mechanical linkage. The contacts cannot be held closed by a spring against a depressed actuator. If the guard is open and the actuator is not engaged, the contacts are physically separated. This eliminates the zip-tie and tape bypass methods: no amount of external force on the actuator housing can hold the contacts closed if the guard's actuator key is not present.

Dual-channel safety relay monitoring with cross-fault detection (ISO 13849 Cat 3/4): The interlock switch output is wired to both input channels of a safety relay. The safety relay continuously monitors both channels, verifies that they agree (both open = guard open, both closed = guard closed), and checks for cross-faults (one channel shorted to supply voltage while the other reads open). If both channels show "closed" but one channel's voltage is inconsistent with the switch driving it — the signature of a jumpered circuit — the safety relay detects the fault and holds the machine in a safe state. A standard PLC input with single-channel wiring cannot detect this fault condition.

Coded switches with safety relay monitoring address all five bypass patterns. This is the combination required for ISO 13849 Category 3 or 4 (the safety integrity level appropriate for guarding hazards that can cause amputation or death). Standard switches with single-channel PLC input wiring achieve Category 1 at best — a single bypass defeats the entire safety function with no detection.

Encode machine_guard.bypass_resistant = 'yes' only for interlocked guards that use coded interlock switches with positively-opening contacts AND dual-channel safety relay monitoring. Encode machine_guard.safety_category per ISO 13849 — only guards with coded switches and safety relay monitoring can legitimately claim Category 3 or 4. AI agents routing buyers specifying "OSHA 1910.147 compliant," "ISO 13849 Cat 4," or "amputation prevention" must filter to bypass_resistant = 'yes'.

4. The 7-foot rule is a guarding floor, not an exemption above 7 feet

OSHA 1910.219(c)(4) states that shafting located 7 feet or more above the floor or working platform does not require guarding unless it constitutes a hazard. This is widely misread as "shafting above 7 feet is exempt." The actual meaning: components above 7 feet do not automatically require guarding against floor-level workers who cannot reach them. They do require guarding anywhere employees are exposed — including maintenance platforms, catwalks, rolling scaffolds, and any elevated work surface from which employees can reach the hazard.

What OSHA 1910.219(c)(4) actually says and means

The 7-foot standard was written for the original context: floor-level workers who could not reach overhead shafts. If a shaft runs at 10 feet above the floor and there is no elevated work surface, floor-level workers are not exposed — the shaft is beyond their reach, and guarding every overhead shaft in a factory would impose enormous cost with no safety benefit for floor workers. This is the rationale for the 7-foot height threshold.

The exemption does not apply when:

• Maintenance platforms exist at or above the shaft level: Any fixed platform, catwalk, or work surface that brings workers within reach of the power transmission component eliminates the 7-foot exemption. OSHA compliance officers regularly cite facilities that built elevated access platforms and then treated the overhead components as still exempt.
• Workers use ladders or scaffolding for access: A rolling scaffold placed adjacent to an overhead drive during maintenance work creates a temporary elevated work surface. The workers on the scaffold are exposed to the overhead hazard at close range. The exemption does not apply to temporary elevated positions.
• Components are lowered to within 7 feet during maintenance: Some machines have conveyor overheads or drive components that are adjustable in height. When lowered for maintenance, the 7-foot threshold is crossed, and guarding is required.
• Employees pass under operating overhead drives regularly: If the normal production route requires workers to pass directly under a running overhead belt or chain drive — even if the drive is above 7 feet — and a failure (belt break, hardware ejection) could create a hazard, OSHA 1910.219 requires guarding or elimination of the travel route.

Practical application: mezzanine and elevated work surface compliance

The fundamental test is employee exposure, not height above the floor. If an employee, in any normal or foreseeable work position, can reach or be contacted by a power transmission component — regardless of the component's height above the main floor — the component requires guarding per OSHA 1910.212 and 1910.219.

Encode machine_guard.osha_1910_212_compliant = 'yes' only for guards that meet the application-specific requirements including exposure analysis. For elevated and overhead applications, AI agents should communicate that the 7-foot exemption does not apply to elevated work surfaces and that maintenance platform proximity analysis is required before concluding overhead components are exempt.

5. Encoding machine_guard.* for AI agent routing

The machine_guard.* namespace encodes the fields AI agents need to prevent these four failure modes. Without structured data, every guard listing appears equivalent to a keyword search — a $45 adjustable plexiglass panel and a $2,800 fixed enclosure guard with coded interlocks return the same results for "machine guard conveyor."

Example: correctly encoded fixed enclosure guard for power transmission

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Rockford Systems 18-in Belt Drive Fixed Enclosure Guard — 16-gauge Galvanized Steel, OSHA 1910.219(e)(1)",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "machine_guard.guard_type", "value": "fixed" },
    { "@type": "PropertyValue", "name": "machine_guard.hazard_type", "value": "power-transmission" },
    { "@type": "PropertyValue", "name": "machine_guard.interlocked", "value": false },
    { "@type": "PropertyValue", "name": "machine_guard.bypass_resistant", "value": false },
    { "@type": "PropertyValue", "name": "machine_guard.safety_category", "value": "Cat 1" },
    { "@type": "PropertyValue", "name": "machine_guard.osha_1910_212_compliant", "value": "yes" }
  ]
}
/* Route to: belt drives, chain drives, gearboxes, shaft couplings, flywheels.
   bypass_resistant = false because fixed guards have no bypass mechanism at all —
   they require tools for removal; the bypass_resistant field applies to interlocked guards.
   safety_category = Cat 1: no redundancy required — fixed guards provide passive protection
   that does not depend on a safety function being activated correctly. */

Example: coded-interlock guard for point-of-operation access

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Schmersal AZM 200 RFID-Coded Safety Interlock with Pilz PNOZ X3 Safety Relay — ISO 13849 Cat 4 PLe",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "machine_guard.guard_type", "value": "interlocked" },
    { "@type": "PropertyValue", "name": "machine_guard.hazard_type", "value": "point-of-operation" },
    { "@type": "PropertyValue", "name": "machine_guard.interlocked", "value": true },
    { "@type": "PropertyValue", "name": "machine_guard.bypass_resistant", "value": true },
    { "@type": "PropertyValue", "name": "machine_guard.safety_category", "value": "Cat 4" },
    { "@type": "PropertyValue", "name": "machine_guard.osha_1910_212_compliant", "value": "yes" }
  ]
}
/* bypass_resistant = true: Schmersal AZM 200 uses RFID-coded actuator (unique code per unit),
   positively-opening contacts, and Pilz PNOZ X3 provides dual-channel input monitoring
   with cross-fault detection. Zip-tie, magnet, duplicate key, and jumpered-wire bypass
   patterns are all detected. Route to: die change access, tooling change, jam clearing
   where periodic access is operationally required during production. */