Emergency Stops, Safety Interlocks, and Guards: Understanding the Safety Devices on a Machine

Three Basic Lines of Defense

Common safety devices on food machinery fall roughly into three categories:

1. Guards and enclosures: Block off hazardous areas so hands can't reach them.
2. Safety interlocks: The machine stops as soon as a cover is opened, and it can't start if the cover isn't properly closed.
3. Emergency stops: When something goes wrong, one press brings the machine to a stop.

The design order is: first eliminate hazards through construction as far as possible, then add guards and interlocks; the emergency stop is the last remedy and can't replace the first two.

Does the Machine Have an Emergency Stop?

Article 45 of Taiwan's Occupational Safety and Health Facilities Regulations (職業安全衛生設施規則) states: power-driven machinery with significant hazards must have a clearly marked emergency brake device in an appropriate location that immediately cuts power and is linked to the braking system, so the machine can be stopped quickly in an emergency. Article 44 also requires each machine to have its own power cutoff device that can't be started suddenly by contact or vibration.

Section 1.2.4.3 of Annex I of the EU Machinery Directive 2006/42/EC also requires machinery, in principle, to be fitted with one or more emergency stop devices (with exceptions for machines where it wouldn't reduce the risk or isn't applicable).

A good emergency stop design usually has:

• A red button on a yellow base with a distinctive shape (commonly a mushroom head).
• Placement where both the operator and bystanders can reach it quickly; long production lines have several along their length.
• A button that latches when pressed and must be twisted or pulled to reset; after resetting, the machine doesn't restart on its own and the start button must be pressed again.

Does Opening a Cover Stop the Machine?

That depends on whether the machine has a safety interlock. In the regulations:

• Article 58 of the Facilities Regulations: Machinery with nip point hazards, and hazardous parts of CNC or other automated machinery, must have guards, enclosures, or interlocked safety doors where the work could be hazardous.
• Article 73: Centrifugal machines must have covers and interlock devices so they can't start unless the cover is fully closed.
• Article 82: Press-forming machines that could be hazardous must have safety doors, two-hand controls, or sensing safety devices; safety doors must prevent the machine from starting when not closed.
• Article 78: Rolling machines with nip points must have enclosures, guide rollers, or interlocked safety guarding devices.

Key design points for interlock switches: they shouldn't be easy to defeat with tape, magnets, or coins; opening the cover should stop hazardous motion before a hand can reach in; and on machines with high inertia, the cover shouldn't open until the machine has completely stopped.

Can Safety Devices Be Removed?

No. Article 327 of the Facilities Regulations requires employers to have workers observe the rule that they must not remove safety and health equipment at will or render it ineffective, and must report to the employer or supervisor immediately upon finding it removed or ineffective. Article 326 states that if an employer needs to temporarily remove a safety device or temporarily render it ineffective, the employer must consider the workers' physical condition and work situation, suspend their work or take other necessary measures, and restore it immediately once the reason no longer applies.

A common situation on the floor: interlock switches are seen as inconvenient for cleaning, so they get bypassed or taped; guards are seen as blocking the view, so they're removed and never put back. These are the causes most often found in accident investigations. If a safety device really does interfere with work, discuss an improvement with the equipment supplier rather than removing it.

Questions to Ask When Buying

• Where are the emergency stop buttons, and how many are there? How are they reset after being pressed?
• Which covers have interlocks? When a cover is opened, which motions stop and which don't?
• Do drive components (belts, chains, gears) have fixed guards? Do they require tools to remove?
• When power returns after an outage, will the machine start on its own?
• Which covers must be opened for cleaning? Once open, how do you make sure the machine can't be started?

The safety devices fitted to each Dong-Yih model aren't listed item by item in the specifications on our website; please call 06-257-4644 or visit our contact information page. For an overall explanation of entanglement hazards, see Entanglement Hazards and Guarding for Mixers, Dough Sheeters, and Rollers; for isolating power during cleaning, see lockout rules.

FAQ

Q: Must a machine have an emergency stop?
A: Article 45 of the Occupational Safety and Health Facilities Regulations requires power-driven machinery with significant hazards to have a clearly marked emergency brake device; the EU Machinery Directive also requires emergency stops in principle.

Q: Does opening a cover stop the machine?
A: It depends on whether there's a safety interlock. Article 58 of the Facilities Regulations requires guards, enclosures, or interlocked safety doors on hazardous parts of machinery with nip point hazards or automated machinery; with an interlocked cover, opening it stops the machine, and the machine can't start if it isn't properly closed.

Q: Can safety devices be removed?
A: No. Article 327 of the Facilities Regulations prohibits removing safety equipment at will or rendering it ineffective; when temporary removal is necessary, Article 326 requires work to be suspended and the device restored immediately once the reason no longer applies.

Q: After pressing the emergency stop, will the machine start again on its own when released?
A: A well-designed emergency stop latches and must be reset manually, and even after resetting, the start button must be pressed again before the machine will run.