Overview - ISO/TR 9172:1987 (Screw conveyors safety guards)
ISO/TR 9172:1987 is an ISO Technical Report (type 3) that supplements conveyor safety standards for continuous mechanical handling equipment. It documents typical hazards associated with screw conveyors - especially trapping and shearing points where the moving screw meets fixed parts or surrounding structures - and provides illustrated examples of guard types and design sheets that meet the general safety requirements referenced in ISO 1819 and ISO 7149.
Key topics and technical requirements
- Hazard identification
- Describes common danger points: between screw and trough, between adjacent screws, at feed/discharge openings, tube entries, shaft bearings, support bars and ground level.
- Guard types and examples
- Closed tubes; fixed solid covers; fixed or removable grid covers; interlocked opening covers; fixed covers with feeding slots; temporary grid covers for cleaning; protective pipes, grids and cone-shaped grills.
- Design and dimension guidance
- Minimum clearances and protective dimensions are given for typical risks (examples in the report include 25 mm, 50 mm and 5 mm clearances depending on whether fingers or hands are at risk).
- Covers and grids must be strong enough for expected loads - e.g., covers that may be stepped on should withstand at least 100 kg/m².
- Specific requirements for guarding inlets/outlets, slit widths, safety distances, and progressive reduction of the screw helix are included to prevent access to danger points.
- Operational safeguards
- Mechanical/electrical interlocks for opening covers; requirements for inlet cones or extended protective pipes at feed ends; protective grills designed to resist the weight of one person.
- Scope limitation
- Presents illustrative solutions that achieve the required safety level without excluding other equivalent protective methods.
Practical applications
- Use ISO/TR 9172:1987 to:
- Identify and document trapping and shearing hazards on screw conveyors.
- Select or design appropriate guards and inlet/outlet protection for bulk-handling conveyors.
- Define minimum clearances and strength criteria for covers, grids and guard-rails.
- Support risk assessments, machine design reviews, maintenance procedures and operator protection measures.
Who should use this standard
- Plant engineers, conveyor and bulk-handling equipment designers, OEMs, safety managers, maintenance teams, and compliance officers tasked with machine safeguarding and workplace safety.
Related standards
- ISO 1819 - Continuous mechanical handling equipment - Safety code (general rules)
- ISO 7149 - Continuous mechanical handling equipment - Safety code (special rules)
Keywords: ISO/TR 9172:1987, screw conveyors, safety code, guards, trapping points, shearing points, continuous mechanical handling equipment, ISO 1819, ISO 7149, conveyor guard design, industrial safety.