4 Common Questions About Zero Energy State & LOTO

By Ersun Hopi, safety project engineer, Rockwell Automation

A common question when learning about lockout/tagout (LOTO) is “What exactly is a Zero Energy State?” The answer might seem obvious at first. But when you apply the definition to the workplace, the complexity quickly builds, and questions arise.

A Zero Energy State is the point at which equipment has been safely isolated from any chances of re-energization or release of residual energy. It helps protect employees from unplanned or inadvertent start-up or equipment movement of equipment while performing maintenance, repairs or cleaning. Said more plainly — it's achieved when you have shut off everything and nothing can hurt you.

Here are four common questions that are commonly asked regardingpeople ask about Zero Energy State.

1. What defines “energy?” exactly? Are there magnitude limits?

Energy is any energy going into, out of, or residing within the equipment.

For example, if you consider a case packer, many people will assume it only has electrical energy. A few others might find the pneumatic line and realize it also should be a part of the LOTO procedure.

However, to truly establish a Zero Energy State on the case packer, the procedure must address all forms of energy, such as hot glue (which may be powered separately), gravitational energy, and kinetic energy generated from moving machine parts. Also, adjacent equipment such as infeed and outfeed conveyors might need to be considered if they could pose a hazard to the authorized employee when servicing the case packer.

Regarding magnitudes, OSHA standard 1910.147 doesn’t set upper or lower limits for LOTO. For the equipment being worked on, all sources of energy must be at a Zero Energy State. The 50V electrical limit you may be wondering about is aimed for electricians working in electrical panels.

In the case packer example, the main 480V disconnect will be locked out, and the glue machine disconnected if it’s separate. But if the electrical panel still has <50V live inside to keep programmable logic controllers (PLCs) from losing their programming, this is acceptable because the procedure is made to work on the case packer, not the electrical panel.

2. How does a Zero Energy State pertain to nonlockable energy sources such as gravity, thermal or kinetic energy?

A Zero Energy State refers to all sources of energy, whether lockable or non-lockable. For instance, if the equipment has the potential for raised loads — such as an elevator or hoist — then confirming your LOTO procedure to address steps to dissipate or neutralize this source will be critical to establishing a Zero Energy State.

What about other nonlockable sources? For kinetic energy, the LOTO procedure must address how to stop rotating components and how to keep them from spinning if there is potential to do so.

For thermal sources like a hot furnace, they’ll need time to cool down. Capacitors also need time to discharge and might need to be grounded to reach a Zero Energy State.

3. Do I have to worry about the equipment’s total weight? Like if they tip over?

If the equipment is designed to lift or raise up, then yes, you do need to account for its ability to store potential energy due to gravity. The LOTO procedure will need to take steps to neutralize that hazard.

If the equipment is tall, but securely installed, then you do not need to worry about the unlikely scenario that someone will unsecure it and tip it over. While that could be a hazard, it is not covered by LOTO. That would be covered under a job hazard assessment for installation, moving or removal of the equipment.

4. What about adjacent processes or equipment — does that play a part?

Yes, it does, especially in a manufacturing line. Equipment before, after or nearby the equipment being worked on may need to be locked out too, if you will be working nearby.

When you're locking out a piece of equipment, you're saying to yourself, “When this LOTO process is correctly applied, I will be safe to work on this equipment without fear of being injured from an unexpected restart or re-energization.”