Under the common law the shipper owes an absolute duty not to deliver for the shipment the goods of a dangerous nature without expressly giving notice that they are of a dangerous nature. It was, however, disputed for many years …
Lord Campbell CJ said in Brass v Maitland (1856) 6 E & B 470, 119 ER 940 at 944:
Where the owners of a general ship undertake that they will receive goods and safely carry them and deliver them at the destined port, I am of opinion that the shippers undertake that they will not deliver, to be carried in the voyage, packages of goods of a dangerous nature, which those employed on behalf of the shipowner may not on inspection be reasonably expected to know to be of a dangerous nature, without expressly giving notice that they are of a dangerous nature.
Per Atking J in Mitchell, Cotts & Co v Steel Bros & Co, Ltd [1916-17] All ER Rep 578, at p.579:
What is the full extent of the shipper’s obligation? It appears to me that it amounts to this, that he stipulates that he will not ship goods which involve the risk of unusual danger or delay to the ship, which the owner does not know of or might not reasonably know of without communicating to the owner facts which are within his knowledge indicating that there is such a risk. I do not say that his obligation is not wider than that.
Per Mustill J in The Athanasia Cominos  1 Lloyd’s Rep 277 at 283-284:
There still remains the problem of identifying the boundary between those risks which the shipowner contracts to bear and those which he does not. One possibility is to draw the line by reference to the proper method of carriage. According to this view, a shipowner who consents to carry goods of a particular description contracts to perform the carriage in a manner appropriate to goods of that description, and thereby assumes all risks of accidents attributable to a failure to carry in that manner.
This is an attractive proposition, for it neatly solves the question of degree to which I have referred, and enables attention to be concentrated on the means adopted to carry the goods. If the carrier proves that he has used the appropriate means, the claim succeeds, without his having to engage in the often difficult tasks of establishing the precise character of the goods, and the precise respects and degree in which they deviated from the norm. Conversely, if his performance has fallen short of what is appropriate, in a manner which is causative of the loss, his claim must fail. This approach also has the theoretical merit of keeping attention focused on the carriage of the goods, which is the subject-matter of the contract from which the liability of both parties mainly, if not exclusively, arises.
This approach will be sufficient to deal with most problems relating to dangerous cargoes, for in respect of the great majority of goods, the normal precautions will suffice to eliminate the risk of carrying normal goods of the description stated in the contract. Leaving outside casualties from wholly extraneous causes, one can say that proper carriage and dangerous nature are opposite sides of the same coin.
There are, however, cases to which this simple analysis cannot be applied: i.e. those where the nature of the goods is such that even a strict compliance with the accepted methods of carriage will not suffice to eliminate the possibility of an accident. Whether consciously or not, seafarers and those who advise them have chosen to adopt methods of carriage which involve an element of risk. No doubt the risk could be eliminated, if those concerned were to provide complex equipment, and enforce rigorous standards of performance. But for practical reasons, they do not. The existence of this gap between acceptable carriage and safe carriage means that there may be cases where an accident is due, neither to the unusual cargo, nor to any short-comings in the carrier, but to simple bad luck.
Who is to bear the risk of accidents falling into this category? In my judgment, the risk must fall on the carrier. By contracting to carry goods of a specified description, he assents to the presence on his ship of goods possessing the attributes of the goods so described; and in the case under discussion, those attributes include the capacity to create dangers which the accepted methods are not always sufficient to overcome.
This leaves untouched the problem of identifying boundaries of this middle area of acceptable risks. I do not believe that any general solution can be attempted: everything will depend on description of the goods in the contracts, the size of the gap between proper carriage and completely safe carriage, the knowledge of means of the carrier as to the existence of this gap, and other matters from which the extent of the carrier’s assent to the running of the risk can be inferred. All that one can say is that the risks must be of a totally different kind (whether in nature or degree) from those attached to the carriage of the described cargo, before shipment of the particular cargo can be regarded as a breach of duty.
In Mediterranean Freight Services v BP Oil (The Fiona),  1 Lloyd’s Rep. 257 at 268 Judge Diamond, QC, identified what a carrier has to prove in order to recover:
In my view it is clear as a matter of construction that if the carrier is able to prove the three matters specified in art. IV, r. 6 then he is entitled to recover compensation from the shipper for the loss sustained by him as the result of the shipment of a dangerous cargo. What the carrier has to prove is
(a) that the shipper shipped goods of an "inflammable, explosive or dangerous nature";
(b) that neither the carrier, the master nor any agent of the carrier consented to the shipment of such goods with knowledge of their nature and character and
(c) that the carrier suffered damages or expenses "directly or indirectly arising out of or resulting from such shipment" (i.e. from the shipment of the goods of the described class).
Per Lord Lloyd of Berwick in Effort Shipping Co Ltd v Linden Management SA (The Giannis NK),  1 All ER 495 at p.506:
The dispute between the shippers and the carriers on this point is a dispute which has been rumbling on for well over a century. It is time for your Lordships to make a decision one way or the other. In the end that decision depends mainly on whether the majority decision in Brass v Maitland (1856) 6 E & B 470, which has stood for 140 years, should now be overruled. I am of the opinion that it should not. I agree with the majority in that case and would hold that the liability of a shipper for shipping dangerous goods at common law, when it arises, does not depend on his knowledge or means of knowledge that the goods are dangerous. An incidental advantage of that conclusion is that the liability of the shipper will be the same whether it arises by virtue of an implied term at common law, or under art IV, r 6 of the Hague Rules.