6.3 Assembly Mechanics: Stringers, Protection & Weight
Key Takeaways
- Ring-handled instruments are placed on a stringer or rack in the open, unlocked position so cleaning and sterilant reach every surface.
- Tip protectors must be vented, sized to the tip, applied to dry instruments only, and never used to hold a bundle of instruments together.
- Heavy instruments go on the bottom and delicate instruments on top, with concave surfaces oriented so condensate can drain.
- The widely applied ANSI/AAMI ST79 guidance limits a wrapped set to 25 pounds, and overweight sets cause wet packs and staff injury.
- Absorbent tray liners, organising racks, and silicone mats are used per their own instructions and must not block steam contact.
Configuration Is a Sterilization Requirement, Not Housekeeping
Every rule about how a tray is physically built exists so that the sterilant reaches every surface and the pack dries. A perfectly counted, perfectly functional set that is configured badly will come out wet, or will not have been sterilized at all in the places that matter.
Ring-Handled Instruments on Stringers
| Rule | Reason |
|---|---|
| Instruments open and unlocked | A closed box lock and closed jaws exclude the sterilant from the mating surfaces; a locked instrument is also under thermal stress and can crack |
| Placed on a stringer, rack, or pin holder | Holds the instruments open and separated, prevents shifting, and keeps them from tangling |
| Curved instruments in the same direction | They nest without crossing and do not lever each other |
| Do not overload a stringer | Instruments packed tightly shield each other from steam |
| Never use rubber bands | They form a complete barrier to the sterilant and are not an acceptable identification method |
| Heaviest at the bottom or on their own stringer | Prevents crush damage |
Protection Devices
| Device | Rules |
|---|---|
| Tip protectors | Must be vented, must be sized to the tip, applied to dry instruments, and used to protect a single instrument tip — never to bundle instruments together |
| Instrument organisers / silicone mats / racks | Hold instruments apart; used per their own IFU; must not create a barrier layer |
| Foam and corner protectors | Only products validated for the sterilization method in use |
| Absorbent tray liners | Used per IFU to manage condensate; the wrong liner or too many liners can hold moisture and cause wet packs |
| Silicone finger mats / brackets | Hold micro and delicate instruments in place |
The recurring theme: every protective device is also a potential barrier. A non-vented tip protector, an oversized protector that seals the tip, a foam pad not validated for the cycle, or an excess of liners all create places the sterilant cannot reach or the condensate cannot leave.
Orientation and Drainage
- Concave items face down or on edge — basins, cups, kidney trays, retractor blades with a hollow — so condensate runs out instead of pooling.
- Lumened items are positioned so the lumen can drain, per IFU.
- Multi-level trays: heavy on the bottom, light on top, with nothing overhanging or resting on the layer below.
- Do not stack instruments into a solid mass. Steam must be able to move through the set.
Density and Weight
Mass is the enemy of drying. Two limits govern:
- Weight. The widely applied ANSI/AAMI ST79 guidance is that a wrapped instrument set should not exceed 25 pounds (11.4 kg) including the container or tray. Overweight sets are the leading configuration cause of wet packs and a leading cause of staff lifting injury.
- Density. Even within the weight limit, a compacted mass of metal in a small tray retains heat and moisture. Instruments must be distributed across the tray footprint, not heaped.
When a set genuinely cannot be built within the limit, the correct answer is to split it into two sets with a documented count sheet for each — not to accept a heavy tray and extend the dry time indefinitely.
Multi-Part and Special Items
| Item | Configuration rule |
|---|---|
| Disassembled devices | Sterilized disassembled per IFU; components kept together and identified |
| Devices requiring loose assembly | Assembled only to the extent the IFU allows |
| Sharps (blades, osteotomes, wires) | Protected and positioned so they cannot penetrate the wrap or injure the opener |
| Telescopes and cameras | Dedicated holders or cases; never loose |
| Powered handpieces | Own case with defined positions; often extended dry time |
| Screw and implant caddies | Positions filled and verified; trials and implants kept separated |
| Rigid containers | Filters/valves checked, gaskets intact, latches functional, container inspected for dents that break the seal |
The Assembly-Table Sequence
A reproducible sequence prevents omissions:
- Confirm the count sheet version is current.
- Lay out the set in sheet order.
- Inspect and function-test each instrument as it is placed (Chapters 7 and 8).
- Verify components — stylets, keys, obturators, caddy positions.
- Place on stringers, open and unlocked, curves aligned, heavy low.
- Apply tip protection to dry instruments only.
- Position concave items to drain; add liners per IFU.
- Verify weight and distribution.
- Place the internal chemical indicator in the area judged least accessible to the sterilant, per policy.
- Complete the count sheet record and any tracking scan that reflects work actually done.
That last qualifier matters: a scan is a record of a completed step. Scanning ahead, or scanning a step someone else will do later, is a falsified record and is treated in the Ethics content area.
Containers, Filters and Liners
Configuration extends past the instruments to the packaging system that holds them, and each element has its own inspection.
Rigid containers are inspected before every use. Check the gasket for cracks, brittleness, flattening, and correct seating; check the latches for positive closure; check the filter retention plates for secure fastening; and check the container body and lid for dents, warping, or damaged edges that break the sealing surface. A new filter of the correct type is installed for every cycle unless the container uses a valve system, and the filter must cover the perforations completely.
Tray liners are used to absorb condensate and assist drying. They must be used according to the manufacturer's instructions — the wrong liner, or too many, can impede steam contact and actually worsen drying.
Tip protectors, corner guards, and instrument brackets must themselves be steam-penetrable and must not clamp so tightly that they exclude sterilant. A protector that fully occludes a tip is a sterilization failure.
Weight, Distribution and Drying
Instrument set weight is limited because heavy sets retain heat and moisture and are an ergonomic injury risk. The widely applied benchmark for a wrapped instrument set is no more than 25 pounds total, and the mass must be distributed evenly across the tray rather than concentrated at one end.
Weight and wet packs are directly connected. A dense, heavy, unevenly loaded tray creates cold spots where condensate forms and cannot evaporate during the drying phase. If a department is seeing repeated wet packs from one specific set, the configuration of that set — its weight, its density, its use of absorbent liners, and whether concave items are draining — is the first thing to examine, ahead of the sterilizer.
Sequencing the Assembly Bench
Work in a consistent order so nothing is left to the end and forgotten.
Confirm the tray and count sheet match and the sheet is the current revision. Inspect and test each instrument as you place it, because assembly is the last inspection point before sterilization. Place heavy items first and low, string the ringed instruments open on stringers or racks, position concave items to drain, add multi-part items disassembled as their instructions require, and place delicate, micro, and lensed items last and on top in their protectors. Add the chemical indicator, verify the count a final time, and complete the labelling and documentation that links the set to you and to the cycle.
Why are ring-handled instruments placed on a stringer in the open, unlocked position?
Which statement about tip protectors is correct?
An instrument set cannot be built within the 25-pound guidance. What is the correct response?