Overview
ISO 21876:2020 - Machinery for forestry: Saw chain shot protective windows - specifies a test method and performance criteria for protective windows fitted to forestry machines that use a chain saw (including modified machines with chain saw attachments). The standard defines how to simulate a saw chain break and measure whether a protective window prevents high‑speed saw chain shots from passing through to protect operators and bystanders.
Key topics and requirements
- Test apparatus and setup: Uses a rig (per ISO 11837 or equivalent) to generate saw chain shots with the saw casing removed; includes a drive unit capable of maintaining saw chain speed and a protective enclosure for safety.
- Cutting attachment parameters: Defines guide bar selection (longest recommended bar), saw chain pitch, number of drive links and a test saw chain speed equal to 1.2× the maximum no‑load speed recommended by the cutting attachment manufacturer.
- Measurement and instrumentation:
- Two shot measurement panels (200 mm ± 2 mm apart) to calculate shot speed and vector.
- Shot indication panel positioned 75 mm ± 2 mm behind the window sample.
- Angle and speed measurement tolerances (shot angle measured to ±1°, speed control ±2 m/s, drive shaft speed uncertainty ±1%).
- Test samples and conditioning:
- Window test sample dimensions: 360 mm ± 20 mm by 1 000 mm ± 20 mm, flat and mounted to limit deflection.
- Test temperature: 20 °C ± 2 °C measured at mid‑thickness; samples preconditioned to homogenous temperature.
- Procedure controls: Pre‑calibration (10 runs without sample), saw chain stopping device positioning, repeatability criteria (shot occurrence and angle consistency) and a specified number of test runs.
- Ancillary requirements: Labelling, test reporting and use of a saw chain stopping device (Annex A). Protective enclosure and safety warnings are mandated.
Applications and practical value
ISO 21876:2020 is used to:
- Validate and certify protective windows for harvester heads, grip saws, carriers and retrofitted machines (e.g., excavators with chain saw attachments).
- Support product development and design verification for manufacturers of forestry machinery glass, polymer windows and guarding systems.
- Provide testing protocols for independent laboratories and compliance bodies to assess operator safety against saw chain shots.
- Inform risk assessments and procurement specifications for forestry operators, fleet managers and safety engineers.
Who should use this standard
- Forestry machine and cutting‑attachment manufacturers
- Component suppliers (transparent protective materials and glazing)
- Test laboratories and certification bodies
- Safety engineers, technical compliance teams and procurement specialists in forestry operations
Related standards
- ISO 11837 - Saw chain shot guarding systems (test method)
- ISO 6814 - Definitions for chain saw‑equipped forestry machines
- ISO 536 - Paper grammage (referenced for indication panels)
- EN 13984 - Plastic/rubber vapour control layers (materials reference)
Keywords: ISO 21876:2020, saw chain shot protective windows, forestry machinery safety, test method, performance criteria, saw chain shot, guide bar, cutting attachment, protective window testing.
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