How much clearance does an explosive storage box cavity need?

Answer: Twenty millimetres on length and width, 30 on height, plus 25 per side for foam.

Is an 8 millimetre wall stronger than 6?

Answer: More impact resistant, but about 16 percent heavier, and the case below carries it.

Is lower surface resistance always better?

Answer: No. Below 10 to the 6 ohm the material turns conductive and discharge concentrates.

Can a large calculated vent area be reduced?

Answer: Only by recalculating free area; nominal is three times the free figure.

What gets left out of most specification sheets?

Answer: Tolerance and method, without which a nominal value is only an intention.

Explosive Storage Box Specifications: Size, Wall and Load

Quick answer: An explosive storage box is specified from the inside out: cavity from the load outline, wall from volume and stack height, then resistance, flame and vent.

Sizing the Internal Cavity
Wall Thickness and Load Ratings
Static Resistance and Flame Rating
Vent Area, Temperature and Humidity
Writing the Specification Sheet
FAQ

1. Sizing the Internal Cavity

Dimensions cannot be added later: a cavity a centimetre short rejects the load, and slack lets it move. Work back from the largest outline.

Start with 20 millimetres of clearance on length and width, 30 on height, since a hand goes in. Foam takes 25 per side, dividers 8; a 600 by 400 by 320 cavity leaves 550 by 350 by 265.

Parameter	Value	Basis
Cavity length, width	Outline + 20 mm	Handling clearance
Cavity height	Outline + 30 mm	Hand access
Wall	6.5 mm, plus or minus 0.5	Volume and stack

The shell is cavity plus wall plus flange; under 25 millimetres of flange the gasket squeezes out sideways at assembly. Tolerances are bilateral, with 2 to 3 percent shrinkage compensated at mid-value.

2. Wall Thickness and Load Ratings

Wall thickness on an explosive storage box follows volume and stack height: each extra millimetre adds about 8 percent weight, carried by the case underneath.

Explosive Storage Box: yellow green long case closed on a ribbed van floor, tan strap across the lid, two latches, centre handle, firewood behind

Below 50 litres, 5 to 6 millimetres works; 50 to 150 takes 6 to 7; above 150, 7 to 8. Past four tiers, a 12 millimetre cross rib costs less than a thicker wall.

Cavity volume	Wall	Stack	Top load
30 litres	5.0 mm	6 tiers	300 kg
80 litres	6.0 mm	5 tiers	400 kg
150 litres	7.0 mm	4 tiers	500 kg
300 litres	8.0 mm	3 tiers	600 kg

Two loads get confused. Top load is the static stack, tiers times weight times 1.5; base load is the pallet reaction, twice the distributed figure. A 24 hour hold leaves under 2 millimetres.

Measure eight fixed points: four wall centres and four corner radii. Rotomoulded parts run thick at corners and thin on flats, so record the minimum.

3. Static Resistance and Flame Rating

Static control is a band, not a switch: surface resistance should land between 10 to the 6 and 10 to the 9 ohm; below that it turns conductive.

Resistance alone is not enough: write decay time, 1000 volts down to 100 within 2 seconds. A compound that passes resistance but decays slowly releases nothing useful.

Flame rating follows the duty: fixed storage takes GB 8624 B1 with an oxygen index of at least 26 percent, and anything that travels adds UL94 V-0. Each step costs 2 to 3 points of retardant.

The two interfere: retardants raise surface resistance, carbon black lowers flame efficiency, so test both together.

4. Vent Area, Temperature and Humidity

Vent area follows volume and temperature swing: across 50 degrees an explosive storage box builds about 7 kilopascals per cubic metre, and the vent must open inside that.

Explosive Storage Box: yellow green case upright on a dark gradient, two same colour latches, recessed handle and round valve fitting, one horizontal rib

Allow 10 square centimetres per 0.05 cubic metre, so 100 litres needs 20 of free area; the membrane passes 30 percent of nominal, making nominal 65.

Parameter	Band	If exceeded
Working temperature	-20 to 55 C	Corner cracks
Working humidity	Under 75 percent	Condensation
Surface resistance	10 to the 6 up to 10 to the 9 ohm	Charge build up
Vent opening	7 to 11 kPa	False opening

Working temperature runs minus 20 to plus 55 Celsius and storage minus 40 to plus 70: below minus 20 polyethylene loses half its impact strength, above 55 the gasket sets.

5. Writing the Specification Sheet

A specification is finished when it can be inspected: every line needs a nominal value, a tolerance and a method. Six millimetres with no tolerance permits 5.2, and no method leaves two parties measuring two numbers.

Sampling runs by batch, one mould and one shift: three cases for the full list, one destroyed. Drop at 1.2 metres on corner, edge and face, then immerse 30 minutes, no water inside.

Keep a change clause: wall, compound or flame changes are re-sampled, since the same grade from a new supplier can differ by 20 percent in impact. Tiers, environment and travel set wall, flame and vent.

Conclusion

Four numbers decide whether the specification holds: cavity tolerance, wall against stack height, the resistance band, and vent area against opening pressure. Each has a basis and a method, and together they make an explosive storage box specification complete.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.