Safe access control for machinery and hazardous areas
Access interlocks are used to reduce risk when workers enter hazardous areas. Their purpose is to eliminate the possibility of energy restoration occurring whilst personnel are in the restricted area. They achieve this by trapping the key that controls the electrical supply once the supply is off.
Access interlocks typically have two parts: a main body, mounted to the stationary portion of the equipment or door frame, and a bolt, mounted to the door or gate. The key is always trapped in the main body of the interlock when the two parts are separated. Only once the bolt re-engages the main body will the key be released.
For over 100 years, access interlocks from Castell, Kirk and STi have been used across a range of industrial access control environments.
An access interlock is the point in a trapped key interlocking system where people enter the hazard. It is fitted to the door, gate or guard leading into a hazardous area and will only open with a key that has been released by first isolating the energy source. While the door is open, that key stays trapped, so the machine or electrical supply cannot be switched back on.
That is what sets an access control interlock system apart from signage or procedure alone: machine access control is built into the hardware. The safe sequence is the only one that works, regardless of training, time pressure or operator memory. A typical sequence has three steps:
Isolate. The energy source is switched off and locked by an isolation interlock, which releases a key.
Exchange. On larger systems, that key is turned in a key exchange unit to release one or more access keys.
Access. The access key opens the access interlock and stays trapped until the door is closed and locked again.
Part body or full body access? Where an operator only reaches into a machine, a single key access interlock is usually sufficient. Where someone will walk fully inside, a dual key interlock with a personnel key is recommended: the operator carries that key into the area, so the door cannot be locked behind them and the system cannot be restarted until they come out.
The Sentric Safety Group access interlock range
The range below brings together Castell, Kirk and STi access interlocks for hinged doors, sliding doors, gates, guards and trap doors, in single key, dual key and switch-monitored versions. Filter by brand or type, or use the selection guide that follows to narrow it down.
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How to choose the right access interlock
Four questions will get you to the right product family. If your application doesn't fit neatly into one of them, our engineers can specify the system for you.
In washdown, corrosive or heavy-use environments, such as food, chemical and pharmaceutical processing, specify stainless steel: the AI-HD, AIS, AIES and EDIX emergency exit access interlock are stainless, and the AI and AIE are available in stainless versions. In dry, non-corrosive settings such as automotive and steel production, the brass KE and KLE are a common choice. For access points on energy equipment, including trap doors and transformer plug-in connectors, the STi Access Lock is designed for the purpose.
4. Do you need monitoring or an emergency exit?
The AIS (single key) and AIES (dual key) add an IP65 safety switch with 1 N/O and 2 N/C contacts rated to 10 A, so opening the door can also stop the machine through its control circuit or trigger beacons and sounders. Where people must be able to get out from inside, the EDIX adds an internal crash bar for emergency exit and is used in fire protection, turbine and offshore applications.
Locking a switch rather than a door? Bolt interlocks such as the Castell KL dual key bolt interlock and the Kirk Type F interlock lock switchgear handles and levers at the isolation end of the sequence, releasing the key your access interlock needs. They are not designed to be fitted to doors or gates, so pair them with an access interlock from the range above.
Applications and sectors
Access interlocks are used wherever people need to enter an area containing moving machinery, stored energy, live electrical equipment and other notable hazards.
Common applications include:
Food and beverage: mixers, fillers, conveyors and packaging lines during cleaning and maintenance, where stainless interlocks withstand washdown.
Pharmaceutical and chemical processing: enclosed machinery and process areas in hygienic or corrosive environments.
Aggregates and mining: crushers, screens and conveyors where access points see heavy, frequent use.
Sentric Safety Group brings together Castell, Kirk and STi, three of the most established names in trapped key interlocking, with more than a century of experience between them. Whichever brand your site already uses, you get one point of contact for expertly designed products meant to work together.
Specification support: our engineers can design the interlock logic and select the products for your site through our Custom Solution Design service.
An access interlock is a key-operated lock fitted to a door, gate or guard that leads into a hazardous area. It only opens with a key that has been released by isolating the energy source, and it traps that key while the door is open, so the machine or supply cannot be re-energised until the door is closed and locked again.
What is the difference between single and dual key access interlocks?
A single key access interlock is used for part body access, where an operator reaches into a machine but cannot be locked inside. A dual key access interlock adds a personnel key that the operator takes into the hazardous area, which prevents the door being locked behind them and the system being restarted until they leave. Dual key interlocks such as the Castell AIE are recommended for full body access.
Access interlock vs trapped key interlock: what is the difference?
Trapped key interlocking is the overall system and an access interlock is one part of it. A trapped key system typically combines isolation interlocks, which lock off the energy source, key exchange units and access interlocks. The access interlock is the component that physically controls entry to the hazardous area.
Which access interlock should I use for a sliding door?
The Castell AIE, AIS and AIES suit both hinged and sliding doors, while the KE and KLE are designed specifically for sliding doors in dry, non-corrosive environments. If the door also needs electrical monitoring, choose the AIS or AIES, which include an integrated safety switch.
Not sure which interlock fits your door, guard or sequence? Our interlocking specialists can review your application and recommend the right products from across Castell, Kirk and STi.
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