What Happened?

While sectioning tissue with a microtome, a researcher sustained a deep laceration to one finger. At the time of the injury, they were examining the position of the sample within the instrument without having engaged the hand wheel brake or hand wheel lock, and without having placed the knife guard over the cutting surface. The finger was caught between the cassette clamp and the knife holder base. The researcher freed their finger, notified their supervisor, and was sent to the emergency room for evaluation and treatment.

What Was The Cause?

• Direct cause: The researcher's finger was caught between the cassette clamp and the knife holder base while adjusting the tissue sample in the microtome, resulting in a deep laceration.
• Indirect causes:
  • Multi-barrier failure — three engineered safeguards were simultaneously disengaged. Microtomes are designed with layered controls precisely because operators routinely need to reach near the blade:
    • The hand wheel brake prevents the cutting stroke from advancing.
    • The hand wheel lock physically holds the mechanism in place against accidental rotation.
    • The knife guard covers the blade edge during any non-cutting activity.
    • Any one of these, correctly engaged, would likely have prevented the injury. All three were disengaged at the time of the adjustment — converting a routine sample-positioning task into a live-blade interaction.
  • Normalization of shortcutting: Engaging and disengaging the brake, lock, and guard for every sample adjustment adds seconds to each cycle. In high-throughput sectioning, operators commonly drift toward leaving safeguards off "just for a quick look." The design assumption — that these controls will be used every time the hand enters the instrument — erodes under production pressure.
  • Line-of-fire / pinch-point hazard inherent to the instrument: Even with the blade not actively cutting, the cassette clamp and knife holder base form a pinch point whenever the hand wheel can rotate or the clamp can shift. The hazard is structural to the microtome, which is why the engineered controls exist.
• Root cause: The operator performed a hand-in-instrument task with all engineered safeguards disengaged. The microtome's safety design depends on the brake, lock, and guard being used every time the hand enters the cutting zone — including for tasks that don't feel like "cutting," such as sample positioning. When the routine drifts to treating those controls as optional, the layered protection collapses to zero, and the pinch-point hazard is fully exposed. 

How Can Incidents Like This Be Prevented?

• Use available safeguards: Engage all available safeguards before manipulating the specimen. 
• Employ dedicated sample-positioning tools (forceps, brushes), so fingers are not the default instrument for adjusting tissue inside the microtome.
• Ensure that "Controls on before hand in" rule is written into the SOP as a hard stop: brake engaged, hand wheel locked, knife guard in place — every time the hand enters the instrument, including for sample positioning, trimming checks, or debris removal.
• Use a cut-resistant glove (ANSI A4 or higher) on the non-dominant hand for all microtome work, including sectioning, sample positioning, blade changes, and cleaning.
• Address throughput pressure directly. If operators are drifting toward skipping controls to keep pace with sample volume, the fix is to adjust expectations or staffing — not to ask individuals to absorb the safety cost.
• Post-incident debrief rather than discipline, focused on what made skipping the controls feel routine.

Resources

• Risk Group Classification for Infectious Agents