The Importance and Value of Stop Time Analysis for Machine Guarding
Cardinal Compliance Consultants, LLC
Environmental Health and Safety Consulting
In industrial environments, safeguarding employees from machinery hazards is a fundamental responsibility—and a regulatory mandate. One of the most critical, yet often overlooked elements in the design and evaluation of machine guarding systems is stop time analysis. This essential process ensures that safeguarding devices, such as light curtains, pressure-sensitive mats, and interlocked barriers, are placed at appropriate distances to protect workers without compromising productivity.
In this article, we'll go over the importance of stop time analysis for machine guarding, what it is, why it matters, and what your responsibilities are.
What Is Stop Time Analysis?
Stop time analysis measures the time it takes for a machine to come to a complete stop after a stop signal is initiated. This is typically expressed in milliseconds and directly informs the minimum safe distance a safeguarding device must be from the point of operation hazard.
For example, if a press takes 400 milliseconds to stop and an operator can reach into the hazard zone in less time, the safety device must be placed far enough away to prevent access to dangerous motion before it ceases.
Why It Matters
Worker Protection
Improper placement of safety devices—too close or too far—can result in ineffective protection or unnecessary interruption to workflow. A properly conducted stop time analysis ensures that safety devices are placed at the exact distance required to protect workers from pinch points, shearing, cutting, or crushing hazards.
1. Regulatory Compliance
OSHA (29 CFR 1910 Subpart O) and ANSI B11 safety standards require safeguarding systems to prevent access to hazards during machine motion. OSHA also cites ANSI B11.19 and B11.20, which both rely on accurate stopping time data to calculate safe distances. A machine without validated stop time analysis may be deemed non-compliant, opening companies to citations, fines, or litigation.
A machine without validated stop time analysis may be deemed non-compliant, opening companies to citations, fines, or litigation.
2. Risk Reduction and Accountability
Stop time analysis supports a quantifiable approach to risk mitigation. Instead of relying on guesswork or generic safety distances, employers use real machine data to engineer safer environments. In the event of an incident, documentation of stop time testing provides evidence of due diligence and engineering control efforts.
3. Supports Modern Safety Technologies
Safety systems like light curtains, laser scanners, and presence-sensing devices depend on stopping time data to ensure Category 3 or 4 performance per ISO 13849-1. Without accurate stop time input, even the most advanced safety devices can be rendered ineffective.
4. Optimize Production Layouts
Overly conservative guarding distances can create workflow inefficiencies or obstruct operator access. With validated stop time data, safety devices can be positioned closer to the hazard where appropriate, maximizing productivity without compromising safety.
When and How to Conduct Stop Time Analysis
Stop time analysis should be conducted:
Using specialized instruments—such as deceleration meters or stop time analyzers—technicians can measure the stopping time at full operational speed. The results are then used to calculate the Minimum Safe Distance using this basic formula (from ANSI B11.19):
D = K × T + C
Where:
Building a Culture of Safety
Investing in stop-time analysis sends a clear message: employee safety is not negotiable. It reflects a proactive and informed approach to hazard control, one that emphasizes precision, compliance, and prevention by providing critical data to:
At a time when companies face increasing scrutiny over workplace safety, incorporating stop time analysis into your guarding strategy is not just smart—it's essential.
Stop Time Measurements for Machine Safety
Stop time analysis is a foundational practice for ensuring machine guarding is both effective and compliant. At Cardinal Compliance Consultants, LLC , we aim to help companies demonstrate professionalism and accountability, by going above and beyond to produce accurate and effective safety standards. If you're unsure if your machines meet compliance or don't know where to start, contact us to schedule a consultation. We don't just calculate stop time analysis for machine guarding, we put practical controls in place to protect workers from whatever hazards they're facing.