Can a workshop floor replace the conditioning chamber?

A: No. Workshop humidity swings between roughly 40 and 75 percent across shifts and cannot hold the plus or minus 5 percent band. Without a chamber, send the samples out.

Is 4 h really enough for a plastic case?

A: It is a floor, valid for walls under 3 mm with no hygroscopic filler. PP filled with talc or wood flour, and assemblies with foam, belong on the 24 h schedule.

Must the test start immediately after conditioning?

A: Within 1 h, with the transfer under 5 min. The longer the gap, the closer the sample drifts back to room conditions and the more of the conditioned state is lost.

Does ISO 2233 cover recovery as well as conditioning?

A: Both ends. Recovery happens in the same atmosphere and ends when mass is stable again, usually within 1 h to 2 h. ---

ISO 2233 Conditioning

Quick answer: ISO 2233 fixes the atmosphere, not the test: 20, 23 or 27 °C at 50 or 65% RH, a 24 h board dwell against 4 h for plastic, judged by mass.

Conditioning is a weighing process, not a waiting room
Three standard atmospheres, and how to pick one
Dwell time depends on the material, and 24 h is only the floor
Rack layout, probes and chamber volume
Stability, then the five minute transfer
FAQ

1. Conditioning is a weighing process, not a waiting room

A 400 x 300 x 200 mm PP case left overnight and one held until its mass stops moving are two different samples. The second has a known moisture content; the first has a known dwell time and nothing else.

That distinction decides whether the drop test that follows means anything. Wet board loses up to 30 percent of its edge crush strength, while a dry PP shell turns brittle and splits at the corner radius. When two labs disagree, the conditioning record is the first place to look.

ISO 2233 specifies an atmosphere, a tolerance, a dwell and a stability criterion, all four on the record sheet. It describes no test method, which is why the clause sits at the front of a report.

2. Three standard atmospheres, and how to pick one

Three combinations are defined: 20 °C with 65 percent relative humidity, 23 °C with 50 percent, and 27 °C with 65 percent. Each carries a tolerance of plus or minus 2 °C and plus or minus 5 percent RH.

ISO 2233 documentation stage: closed black hard case on a dark wood conference table, silver laptop left, glass of water right, skyline beyond

Selection follows the test standard that comes next, not preference. Most transport packaging work uses 23 °C/50 percent, humid-climate projects move to 27 °C/65 percent, and some European board clauses sit at 20 °C/65 percent.

The three are not interchangeable. The same 400 x 300 x 200 mm shell holds 0.3 percent moisture at 23 °C/50 percent and 0.5 percent at 27 °C/65 percent: wall thickness holds, stiffness does not.

3. Dwell time depends on the material, and 24 h is only the floor

Twenty-four hours applies to paper and board. Plastics absorb slowly and little, so 4 h is enough above a 3 mm wall; plywood and timber, with higher starting moisture, often need 48 h. A shell with a foam liner follows the slowest layer.

Material class	Minimum dwell	Weighing interval	Typical risk if short
Paper and board	24 h	24 h	edge crush reads high
Corrugated board	24 h	24 h	compression reads high
PP, ABS, PC shell	4 h	12 h	corner cracking in drop
Foam liner, EVA	6 h	12 h	false rebound
Plywood, timber	48 h	24 h	mass drift after test

Dwell and stability are separate conditions, and both must be met: dwell is time in the chamber, stability is mass that has stopped drifting. Meeting the first without the second is half a procedure.

The atmosphere and the dwell belong on the request form, not in the technician's judgement. When a customer asks for 48 h, the report states 48 h, not a rounded 24 h.

4. Rack layout, probes and chamber volume

Keep 100 mm between samples, 500 mm from the chamber wall and 100 mm off the floor, never in front of the supply duct. The clearances let air move around every face instead of drying one side.

Probe position matters as much. Place the sensor between samples, 200 mm clear of the nearest one, away from wall and return grille. A probe on the wall reads the wall, typically 1 °C to 2 °C below the air, so the chart looks compliant while the sample is not.

ISO 2233 sampling point: moulding shop with blue production-area sign, green carton racking, white machine behind yellow rails, red overhead crane

Chamber volume should be at least five times the sample volume: a 60 L case wants 300 L of usable space, and three cases need 900 L. Every door opening costs about 40 min of recovery, and an undersized chamber lets samples push local humidity past 70 percent, which the chart may not show.

5. Stability, then the five minute transfer

Stability is judged on a balance, not on the dial. Two consecutive weighings, at least 24 h apart, must agree within 0.1 percent of sample mass. If both differ by more, the next check waits another 24 h.

Weigh on the same balance each time, at 0.1 g resolution, and put the sample back within 1 min. Each opening drops humidity by 3 to 5 points and needs 20 min to recover, so plan the schedule before the batch starts.

Log temperature and humidity every 15 min. A continuous excursion beyond tolerance for 30 min voids that stretch and restarts the clock; a 1 to 2 min door event can be noted.

From the last weighing to the test start, the chain must fit inside 1 h, transfer under 5 min. Move the case flat, never stacked, never in sunlight.

Stage	Limit	Permitted action
Removal	door closed within 1 min	take only the scheduled sample
Transfer	5 min or less	carry flat, no stacking
Set-up	10 min or less	mount in test attitude
Test start	within 1 h of removal	go straight into the next procedure

The recovery leg is usually skipped, yet ISO 2233 treats it as the mirror of conditioning. A dropped case goes back into the same atmosphere for 1 h to 2 h before inspection; otherwise the shell relaxes, cracks close up, and the defect rate comes out too low.

Anything beyond 1 h belongs in the report as an actual interval, with a note that conditions may have drifted. The same shell dropped 3 h after removal cracks at the corners more often than one dropped within the hour.

Conclusion

The useful part of ISO 2233 is not the table of atmospheres but the numbers around it: three conditions, a tolerance of plus or minus 2 °C and plus or minus 5 percent RH, 24 h for board against 4 h for plastic, two weighings within 0.1 percent, a 5 min transfer and a 1 h window to start. Write those into the work instruction and conditioning stops being a formality. Only samples that dwell long enough, weigh stable and travel fast produce comparable data.

This article covers case-side specifications only and does not address any handling, loading or use of the contents.