A FIFO lane is a controlled queue between processes that preserves first-in, first-out sequence while limiting the amount of work-in-process allowed between them.
FIFO stands for First In, First Out.
The oldest item in the lane should be the next item processed downstream.
Why FIFO is useful
Processes cannot always be directly connected in one-piece flow.
A controlled queue may be needed because of:
- different cycle times;
- physical separation;
- shared equipment;
- batch constraints;
- process variability.
The FIFO lane provides a defined buffer without allowing unlimited WIP.
Preserve sequence
Sequence matters when age, traceability, order priority, or material condition can deteriorate over time.
A visible FIFO lane makes it harder for newer work to jump ahead of older work without a deliberate decision.
This can reduce:
- hidden aging;
- forgotten orders;
- material expiration;
- traceability confusion.
Limit the queue
The lane should have a defined maximum.
When the downstream process cannot consume work and the lane becomes full, upstream should not continue producing indefinitely.
This connects with Pull Systems, because production should respond to downstream capacity rather than push unlimited inventory forward.
FIFO vs supermarket
A Supermarket Pull System holds controlled inventory by part or container and uses replenishment signals.
A FIFO lane controls sequence through a queue.
Use FIFO when preserving order and limiting WIP are the primary needs.
Use a supermarket when controlled replenishment by item is required.
Connect to Little’s Law
Little’s Law connects WIP, throughput, and lead time.
If throughput remains unchanged, more WIP generally means more time in the system.
A FIFO lane makes the WIP limit physical and visible.
Design the lane
Define:
- entry point;
- exit point;
- direction of flow;
- maximum capacity;
- unit or container size;
- abnormality response;
- responsibility.
The physical design should make the correct sequence easy.
Manage a full lane
A full FIFO lane is an abnormal condition.
The response should be defined.
Possible actions include:
- stop upstream release;
- investigate downstream blockage;
- escalate equipment or quality problems;
- rebalance work;
- recover flow.
Do not silently create overflow inventory beside the lane.
Common mistakes
Using FIFO without a WIP limit, allowing sequence jumping, creating unofficial overflow areas, using the lane as permanent storage, and increasing capacity instead of solving recurring blockage are common mistakes.
Practical sequence
- define the process connection.
- determine why direct flow is not practical.
- define the required FIFO sequence.
- set a WIP limit.
- design visible entry and exit.
- define abnormality rules.
- train the users.
- monitor full-lane events.
- solve recurring downstream constraints.
- reduce WIP as stability improves.
The practical lesson
A FIFO lane creates discipline between processes.
It protects sequence and makes excess WIP visible instead of allowing inventory to grow without control.