Modular Desk System for Earthquake-Prone Schools
A Wellington furniture manufacturer has designed a modular desk for intermediate schools in an earthquake-prone region. The desk uses 18 mm medium-density fibreboard panels with a powder-coated steel frame and is assembled on site with a rubber mallet and six cam locks. The design brief requires tool-free assembly in under four minutes by one caretaker, a mass under 18 kg per desk to reduce injury risk during evacuation, and a fire rating of at least Group 2 when tested to NZS 3838. Prototype testing found: assembly time averages 6 minutes 40 seconds, mass is 22.4 kg, and the fire test failed because the exposed MDF edge seal smoked excessively in the first 90 seconds. The manufacturer has orders from three schools for 420 desks and a fixed delivery date in 11 weeks. Switching to a different panel material would add NZD 19 per desk, and the schools have not agreed to a price increase. The production manager must decide whether to redesign the panel, change the frame, or renegotiate the brief.
1. Assess which brief constraint is most at risk of causing the whole project to fail, and explain your reasoning using the test evidence.
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The most at-risk constraint is the fire rating, because it is a compliance failure rather than a performance shortfall. Assembly time at 6 minutes 40 seconds is over the four-minute target but can be addressed by process changes, extra cam locks, or a different joint; mass at 22.4 kg can be reduced by thinning panels or changing the frame, though both affect stiffness. The fire test failure, however, is binary: if the desk does not meet Group 2, it cannot be installed in the schools under the building consent. The smoked MDF edge is also a symptom that the exposed core is the problem, not the coating, so edge sealing alone may not fix it. The 11-week delivery date and 420-desk order mean there is limited time for a full retest cycle, which typically requires sample preparation and an accredited laboratory slot. Therefore, the fire constraint should drive the redesign decision. The manager should not treat the fire test as a detail to be fixed after delivery; it is the gating item. If the fire rating cannot be achieved with the current panel, the project needs a material change or a renegotiated brief, and that decision must be made immediately.
2. Compare two redesign pathways and recommend one, considering cost, schedule, and the brief constraints.
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Pathway one is a material substitution: replace MDF with a fire-retardant treated particleboard or a mineral-core panel, keep the steel frame, and redesign the cam-lock positions. This would likely meet the fire rating because the core chemistry is different, and it could reduce mass if a lower-density core is chosen. It adds NZD 19 per desk, which is NZD 7,980 across the order, and the schools have not agreed to a price increase, so the manufacturer would absorb the cost or negotiate. It also requires a new fire test, which may take three to four weeks, leaving little margin in the 11 weeks. Pathway two is a frame and panel redesign: keep MDF but change the edge detail to a fully encapsulated steel channel and add intumescent strips, then retest. This might be cheaper per desk but is less certain to pass, because the MDF core still contributes fuel. It also does not address mass or assembly time. I recommend pathway one, with a parallel negotiation: offer the schools a choice between accepting the NZD 19 increase or reducing the order to 300 desks to stay within budget. The material substitution is more likely to pass the fire test first time, and the mass reduction may also help meet the 18 kg target. The schedule risk is real, so the manufacturer should book the fire test now and expedite sample production. Pathway two risks a second failed test and a missed delivery date, which would be worse than a price negotiation.
3. Explain how you would test the redesigned desk against the brief before shipping, and what evidence would convince the schools to accept the change.
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The test plan should mirror the brief's three constraints and add a usability check. For fire, the manufacturer must commission an accredited test to NZS 3838 on the final production specification, not a prototype, and provide the full test report including smoke development and heat release. For mass, weigh 10 randomly selected production desks and report the mean and range; the target is under 18 kg, and the evidence should show the upper confidence limit below 18 kg, not just an average. For assembly, run a timed trial with six caretakers who have not seen the desk before, using the written instructions, and record completion time and errors. The target is under four minutes, so the evidence should show the 90th percentile under four minutes, because a single fast assembler is not convincing. For durability, cycle the cam locks 50 times and check for loosening. To convince the schools, the manufacturer should present a comparison table of old and new performance against each brief constraint, the fire certificate, and a cost-sharing proposal. The schools will care most about safety and disruption; a demonstration where a caretaker assembles the desk in front of them, plus the fire certificate, is more persuasive than a written report. If the mass is still above 18 kg, the manufacturer should offer a wall-mounted storage option or a two-person lift instruction, but that weakens the brief and should be negotiated openly.