Safety stock
Safety stock is the buffer quantity of a part held above expected demand to absorb supplier delays, demand spikes, or quality rejects without stopping production. The planning team usually sets it. The buyer lives with the consequences when it is set wrong (or set to zero) and a delivery slips.
Part of the Procurement Glossary
How it works in practice
Planning sets a safety-stock target on a part: 2 weeks of demand, or 100 units, or some calculated figure that factors in lead-time variability and demand variability. The MRP system then plans against expected demand plus the safety-stock cushion, so the buyer sees the cushion as part of the suggested order quantity, not as a separate line item.
For the buyer, safety stock is mostly invisible until something slips. A part with two weeks of safety stock can absorb a supplier delay quietly: the line keeps running while you chase the late delivery. A part with zero safety stock turns every late delivery into a line-down conversation. The two parts can sit next to each other in the ERP and feel completely different on the floor.
A senior buyer reads safety-stock policy as risk distribution. The parts with the most cushion are the ones planning has decided can absorb a slip; the ones with no cushion are the ones planning is betting will arrive on time. Knowing which is which changes how you triage the open-PO list.
Why it matters
Safety stock is the difference between a delivery surprise and a line-down. When a supplier misses by a week on a part with three weeks of cushion, you have time to recover. When the same supplier misses by a week on a part with no cushion, you are in firefighting mode immediately. The same delivery slip has very different downstream costs depending on where the safety-stock policy lands.
For the buyer, the actionable point is awareness. You will not be the one resetting the safety-stock target, but you will be the one calling the supplier when a no-cushion part is at risk. Knowing which parts have buffer (and which do not) is what turns the same open-PO list into a sensible priority order.
Tips
Know which of your parts run with no cushion
Ask planning for the list of parts at zero or near-zero safety stock. Those are the ones a single supplier slip can stop the line on. Treat them with more attention on the open-PO list than parts with weeks of buffer.
Use safety stock as triage signal, not policy
Do not try to override safety-stock policy as a buyer. Use it as input: when two parts are equally late, the one with less cushion gets the call first.
Flag chronic safety-stock breaches back to planning
If you keep firefighting the same part because the cushion is set too low for the actual lead-time variability, that is a signal worth feeding back. The buyer sees the variability data planning needs to recalibrate.
How PO-Relay helps
PO-Relay shows the live state of every open PO so you can see what is on order, what is at risk, and what is already late. The Parts Dashboard makes it easy to filter by supplier, by part, or by problem flag, so when a delivery slips you can quickly see whether the at-risk part has cushion behind it or not. The morning briefing surfaces the at-risk loops at the start of the day.
PO-Relay does not calculate safety stock or hold the policy targets. The math (Z-score, demand and lead-time standard deviation, service-level targets) and the resulting on-hand targets stay in your ERP or planning system. PO-Relay's contribution is keeping the open-PO list honest so you know which deliveries are about to test the cushion.