Acid next to hypochlorite in a hot pantech
Townsville, 38 °C, and a hardware distributor is loading a 10-pallet rigid pantech for a three-drop run. The load: eight 15 L drums of UN 1789 hydrochloric acid 33% (Class 8, PG II); four 25 kg pails of UN 2880 calcium hypochlorite, hydrated (Class 5.1, PG II) for the first drop, a pool shop; twelve 20 L drums of UN 1133 adhesive, Class 3, PG II; and two 25 L containers of isopropanol, Class 3, PG II. The yard hand's plan is to put the acid and the hypochlorite side by side at the front of the body 'so the chemicals are together', load the adhesives hard against the rear doors 'to save time at the pool shop', and rely on the pallets being heavy enough not to move. The pantech has a loose plywood bulkhead behind the cab and no load-restraint straps on board. Nobody has checked the segregation chart or the load restraint guide.
1. Assess the proposed stowage of the acid, the hypochlorite and the Class 3 goods. What must change, and why?
Read the worked answer
The segregation chart is the floor, not the whole answer. Work out the chart result first, then apply the chemistry.
Hypochlorite (5.1) with acid (8). The chart requires separation, but the practical reality is decisive: acid plus hypochlorite liberates chlorine gas. One weeping acid drum running onto a pail of hypochlorite turns a small spill into a toxic gas cloud inside a closed pantech - and then into the cab. Side by side on the floor at the front is the worst possible arrangement. The answer is not 'a bit further apart': they should not travel in the same vehicle body on this run. Split them onto separate vehicles or separate runs.
Hypochlorite (5.1) with Class 3. The chart requires segregation - a minimum separation or an intervening barrier - and oxidiser plus fuel is a genuine fire pair. A leak plus a spark is all it takes.
Acid (8) with Class 3. Corrosive plus flammable: keep them apart so a leak cannot pool under the drums.
What should actually be loaded: the Class 3 goods together, upright and low; the acid separated at the rear behind a barrier with its labels facing out; the hypochlorite on a different vehicle. Heavy drums low, closures up, nothing stacked above a corrosive that can leak down onto it.
2. Is the load restraint adequate? What would you require before the vehicle leaves, taking account of the drop order?
Read the worked answer
No. There are three defects and one planning error.
The loose plywood bulkhead. A bulkhead only helps if it is secured and rated to take the forward load. Loose, it is a projectile under 0.8 g braking - the standard the load must survive - and it will not stop a 200 kg pallet.
No straps, no dunnage. 'Heavy enough not to move' fails at the first roundabout. Each pallet must be restrained to the body itself, not to its neighbour, using rated straps or load bars to rated anchor points, with edge protection, or blocked in against a rated headboard. Pallets must be banded or wrapped so the drums cannot walk off them.
The drop order is backwards. The hypochlorite for the pool shop is the first drop, but the plan buries it at the front of the body behind twelve drums of adhesive. The driver would unload and reload the entire vehicle in a customer car park, in 38 °C heat, with corrosive and oxidiser packages. Load last drop forward, first drop at the doors.
Before departure: correct placards fitted (this is a placard load), the DG transport document on board, the driver briefed on what is where, extinguishers in place, and a written check that the restraint has been physically tested by hand before the doors close.
3. What is the heat doing to this load, and what controls apply?
Read the worked answer
38 °C ambient in Townsville, and a closed pantech standing in the sun sits well above ambient - often 50 °C or more. There are two different effects.
Calcium hypochlorite (5.1). It decomposes with heat, and decomposition releases chlorine and oxygen and generates more heat - a self-accelerating loop inside a confined space. It must be kept cool, dry and ventilated, away from acids, organics and anything combustible. A closed pantech is the wrong environment for it, which reinforces the decision to send it on a separate vehicle or at minimum with ventilation and shade.
Class 3 drums. Heat raises vapour pressure. A drum that is overfilled or has a swollen bung will weep, and a weep next to an oxidiser is the fire scenario. Drums upright, closures up, bungs tight, ullage correct, not jammed against a hot metal floor or wall.
Controls: load early or late rather than at midday, park in shade where possible, ventilate the body, and brief the driver on recognising chlorine - a sharp bleach smell, coughing, watering eyes. The response is to stop, get upwind, keep others back and call 000. He must not open the doors into a suspected chlorine atmosphere to see what is happening. The spill kit and PPE should include eye and respiratory protection appropriate to both classes on board.