Gwaith Powdwr

Two-ton ballistic pendulum


24 July 2011

Gwaith Powdwr, Penrhyndeudraeth

SH 61637 38864; 52.92929°N, 4.05986°W


Gwaith Powdwr is a post-industrial nature reserve owned by the North Wales Wildlife Trust and located in Penrhyndeudraeth near Porthmadog. The site — formerly an explosives manufacturing works — covers an area of 28 hectares spread over three valleys of heath, scrub and woodland habitat.

Production of explosives at the site dates back to 1865 and the works there were destroyed by a massive explosion in 1915. In the 1920s the site was acquired by Cooke’s Explosives Ltd, which was, in 1958, to become a subsidiary of ICI. Production finally came to an end in 1995 and three years later ICI donated the site to the North Wales Wildlife Trust.

Cooke’s Explosives also made use of the disused slate quarry at Croesor as a storage facility for its products.

The text given below has been reproduced from the information panels provided by the North Wales Wildlife Trust at the site.

Gwaith Powdwr (North Wales Wildlife Trust);
Gwaith Powdwr (BBC, North West Wales);
Croesor Quarry

Cooke's Explosives Ltd entrance gates

Safety wall

Gwaith Powdwr

Explosives shed behind safety wall

"Floating" roof of explosives shed - designed to blow off in the event of an explosion

In these sheds, workers wrapped the explosives and sealed them in wax to protect them from the damp. Working with explosives was dangerous and each shed had many safety features to limit the risk of an explosion on site. Having a lead floor helped prevent sparks. Sheds were built some distance apart and surrounded by a thick wall of earth and sandbags and the roof of each shed was “floating”, thus enabling the blast, should an explosion occur, to be directed upwards rather than sideways.

All these safety measures were designed to prevent a chain reaction of explosions spreading between sheds and avoid a repetition of the devastation that occurred in 1915.

In some parts of the site the explosives and raw materials were moved from shed to shed using a system of aerial pulleys, as some areas were too steep or uneven to use trucks on rails.

Magazine incline and winding house

Winding house

Winding house

Water tank

Gwaith Powdwr

Pendulum Shed

The manufacture of explosives on this site dates back to 1865. The geology of the area, with two long rock ridges, which divide the site into three distinct areas, made it an ideal location as they reduced the risk of accidental explosions spreading.

The steep slopes on this side of the site, overlooking the Dwyryd Estuary, were ideal for the production of Nitroglycerine as the materials could be moved by gravity, a safer method than pumping.

There have been many owners, including, during the First World War, the Ministry of Munitions under the control of David Lloyd George. After the First World War the works were purchased by R T Cooke, who extended the works on this site by transferring his other company ‘The Miners Safety Explosives Co.’ here. During World War Two the site produced 5,000 tons of military explosives a year, as well as filling 17 million grenades.

In 1958, when R T Cooke retired, ICI took full control of the site. After transferring the manufacture of “Permitted Explosives” required by the National Coal Board to the site in the 1960’s the site became prosperous. These explosives contained flame retardant chemicals, including salt, which made them safer for use in gas filled coalmines. Other sites had failed to produce explosives of the right quality and the success of the Penrhyndeudraeth works was commemorated in the explosive’s names; PENOBEL 1 and 2, coming from PENrhyndeudraeth and nOBEL. The Ballistic Pendulum was essential in gauging the strength of these “permitted explosives”.

The Ballistic Pendulum in this shed was used up until 1983 to calculate the explosive strength of the powder or gel produced on the site. A charge of explosive was placed in a cannon, which was then pushed up against the cavity in the pendulum. The explosion would cause the pendulum to swing, while a pointer would record the force of the blast on a scale.

The Nitroglycerine production area came to be known as Klondyke by the workforce. Materials, including glycerine and glycol plus nitric acid and sulphuric acid pumped from the middle valley were mixed and then tested to establish their stability. What is now the bird hide once housed a series of 7 settling tanks where excess Nitroglycerine was removed from the washing water. Further ingredients were then added to the mixture to produce powder or gel based explosives, which were then transported to the middle valley for catridging. The cartridges were passed through liquid wax for sealing from moisture, before being stored in secure magazine buildings. Many of the factory’s buildings had safety features such as lead flooring, reducing the risk from sparks.

Production of complex “Permitted Explosives” peaked in the 1970’s, when the site was considered the most sophisticated operation of its kind in the world. Work finally ceased in 1995 following a decline in the demand for Nitroglycerine based explosives. The area was decontaminated and decommissioned before being handed over to the NWWT in 1998.

Ballistic Pendulum

Ballistic Pendulum

Ballistic Pendulum

Dipping pond

This pond was used to store cooling water, an essential part of the safe manufacture of nitroglycerine based explosives. Before the automation of the cooling process the temperature of the nitroglycerine had to be constantly monitored [by an operator sitting on a one-legged stool to prevent him from falling asleep].

Commemorative plaque

Commemorative plaque

Afon Dwyryd and the Harlech Toll bridge (Pont Briwet), with Harlech Castle on the horizon

Belfast Store

This is one of the best examples of this type of building that exists anywhere. The roof is especially notable — an arch of wood that would lift off easily if there were an explosion.

This was where they stored the explosives before moving them to the quay to be exported. As with the explosive sheds, there are many safety features; the leaden floor, to minimise the risk of sparks, the distance of the building from the main site, which would have limited the effect of an explosion and a thick metal door with a substantial lock with, on the inside of the keyhole, a cover to stop sparks jumping through and causing an explosion.

It was imperative that the store was kept grit free as grit could cause sparks, so workers wore special shoes here. On the shed there was also a lightning conductor, because lightning strikes were a frequent cause of explosions.

Emergency shelter

Here and there, dotted amongst the site, there are a number of emergency shelters. When the alarm sounded the workers would run to the shelters to take cover. Thankfully explosions were infrequent and after a time they could return to their work.

These structures have now been adopted by wildlife, especially the rare Lesser Horseshoe Bats that use these “caves” as roosts in the summer and for hibernation in the winter.


7 thoughts on “Gwaith Powdwr

  1. Pingback: Croesor Quarry « GeoTopoi

  2. What a fascinating site, interesting that there is so much left. Most explosive sites are completely cleared (ROF Chorley near where I live being a good example), although ROF Wrexham / Marchweil) still has some buildings left standing even though it’s been closed for many many years.

    • Yes, I think the NWWT have done a splendid job in creating and maintaining the nature reserve at the site, incorporating some of the original structures. I was particularly interested in seeing the ballistic pendulum there.

  3. What a brilliant set of photographs from this wonderful site. We went round one afternoon last spring but didn’t manage any images as good as these. The header shot with the mouth of the cannon is super, really abstract and thought provoking. I have earmarked that shot of yours of Pont Briwet as a good location to capture next years’ “Plandampf” …although the new bridge construction may put a spanner in my works! Really fascinating and superbly illustrated post, Graham.

  4. Does anyone have any historical information on the factory when it was operating? I am interested in knowing what sorts of raw materials were brought in and how, and also what was exported and how it was transported. Was there a connection to the Cambrian railway, and what sort of loading/unloading facility and sidings were used? Or was it all done by ship? Are there any site plans or drawings/photos of any part of the works during its operating heyday?
    Who would have this sort of information?

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