Die blocks (also known as safety blocks, press blocks, or maintenance blocks) are a critical safety control used on mechanical and hydraulic power presses. These blocks prevent unintended ram or slide movement during maintenance, die changeover, setup, or inspection activities—protecting workers from crush and amputation hazards.
This guide explains OSHA requirements, applicable ANSI standards, engineering considerations, and best practices to support workplace safety and compliance.
Why Safety Blocks Are Required
Whenever a worker’s hands or body enter the die area of a mechanical or hydraulic power press, OSHA requires the use of a positive mechanical blocking device. Safety blocks prevent the press ram from closing due to:
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Stored mechanical or hydraulic energy
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Gravity-related drift (common in hydraulic presses)
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System failure or unintended actuation
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Electrical or pneumatic control malfunction
By locking the ram in a secure position, die blocks serve as a reliable hazard-control method during servicing tasks.
OSHA Requirements
OSHA mandates the use of safety blocks any time dies are being adjusted or the press requires maintenance:
Key Citation:
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29 CFR 1910.217(d)(9)(iv): Employers must provide and enforce the use of safety blocks during die adjustment or repair.
While OSHA does not define specific size or material requirements, the blocks must be capable of preventing unintended closure under maximum load or drift potential for both mechanical and hydraulic systems.
ANSI Requirements
ANSI standards provide additional design, engineering, and functional guidance for safe press operation.
Relevant standards include:
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ANSI B11.1 – Mechanical Power Presses
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ANSI B11.2 – Hydraulic Power Presses
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ANSI B11.19 – Performance Requirements for Risk Reduction Measures
ANSI requires that safety blocks:
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Be able to withstand the full load of the press
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Be tall enough to fully prevent tool engagement
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Be clearly and permanently load-rated and labeled
For hydraulic presses, ANSI explicitly addresses the need to protect against hydraulic drift, which can slowly lower a ram over time—making safety blocks especially critical.
ANSI also recommends that safety blocks be interlocked with machine controls when feasible.
Sizing and Engineering Considerations
While neither OSHA nor ANSI specifies dimensions, blocks must be engineered to support the full force potential of the press.
Key engineering variables include:
| Factor | Mechanical Press Impact | Hydraulic Press Impact |
|---|---|---|
| Press tonnage | Determines peak load capacity | Determines static + drift-resistance capacity |
| Shut height & die space | Sets block height | Same, plus drift clearance |
| Material strength & compression limits | Ensures fail-safe support | Helps resist gradual load shifting |
Safety blocks should be:
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Permanently labeled with load rating
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Designed for the specific press or press group
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Routinely inspected for cracks, wear, or deformation
Interlock and Disconnect Considerations
OSHA does not require an interlocking system with safety blocks. However, ANSI strongly recommends integrating safety blocks into the control system for both mechanical and hydraulic power presses.
Best Practice:
Use blocks with a limit switch or safety contact tied to a safety-rated control circuit (Cat 1–3). This prevents the press from cycling or energizing hydraulics until:
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The blocks are fully inserted AND
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The blocks are safely removed after servicing
This reduces human error and significantly enhances compliance and press safety.
Best Practices for Safe Use
To ensure consistent and compliant application:
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Store blocks at or near each press
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Use bright colors and clear labeling (e.g., load rating, press ID)
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Train operators and maintenance personnel on:
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Placement and removal procedures
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Press-specific load and height requirements
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Hydraulic drift hazards
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Use interlocked or keyed block systems whenever possible
Facilities with multiple presses frequently standardize sizing and storage locations to improve consistency and reduce misuse.
Summary
Die blocks are required by OSHA when performing maintenance, setup, or repair on both mechanical and hydraulic power presses. ANSI provides further guidance on load rating, labeling, design expectations, and the recommended use of interlocked systems. Proper engineering, operator training, and documented procedures ensure compliance, reduce injury risk, and strengthen safety culture.
