Lecture text for St Catherine's Monastery, Sinai

[1] The Monastery of St Catherine encloses the burning bush observed by Moses. It was founded in the sixth century by the emperor Justinian. The lower walls and the church are in granite. It contains one of the most ancient libraries in the world. Enthusiasts for risk analysis will note the good climate for preservation but be dismayed at the unpredictable uniqueness of the prime reason for the library's survival - a letter from the prophet Mohammed giving the monastery his guarantee of eternal protection.

[2]Let us take the climatic advantages first. Here is the location of the monastery in the high mountains of the desert of Sinai.

[3]Closing in, we can see that the monastery is in a deep valley. Hardly ideal for a fortification. More about that later.

[4]The straight valley channels the wind into only two directions, up and down. The desert sand is here angular quartz fragments from the weathering of the granite mountains. It is very abrasive and this, together with the isolation of the monastery, gives us our first local consideration as we develop a specification: the archive must be airtight, whether it is air conditioned or not. And if there is air conditioning, the particle filtering is much more important than pollutant filtering.

[5] The present library dates only from 1951, in neo Roman style. It is made of reinforced concrete which is decaying fast, with no hope of outlasting the massive granite walls from the 6th century. The library is at the top of the far end of the building.

[6] The library roof is flat, and therefore lets in the very occasional rain and melting snow. However, the plans for rebuilding the library call for a low pitched roof in tile, to give a more romantic view to pilgrims descending from mount Sinai by the steep path down the mountain. So here is another design consideration: the placing in a deep valley and not so far from the tropics, means that the heat gain from direct sunlight is through the roof only. The north wall is shaded by an arcade, as we saw in the previous slide; the south wall is hardly irradiated by the high sun in summer and shaded by the mountain from the low sun of winter. The east and west exterior walls are remote from the library room, as we shall soon see.

[7]This is the present library. A utilitarian space which is to be replaced by a much grander room. This brings in another design factor: the room will be shown to visitors, on guided tours only.

[8]Here is the plan. The main library is the large room in the middle. The reading room is to the east (left), still sheltered from the solar heated east wall by a narrow room. The library is tall - 6 m high. This is a significant measurement because it means that even when it is full of visitors, there will be a large air volume above them.

[9]This is the wire frame model which we used for the computer simulation of the library climate. The program we used is BSim, as already described earlier. The library climate is most influenced by the ceiling, with the weather above, slightly moderated by the open attic structure with tile roof. Its climate is also influenced by the floor, under which the monks have their cells. At present they have paraffin stoves for heating, but, the risk analysis experts will be pleased to know, these will be replaced by central heating.

[10]The climate is unusual. These data were collected by father Justin, a very up to date monk from Texas. The temperature cycles from about 4 to 30 degrees, with a distinctive flat top to the summer temperature. The RH is very low, from 3% to 70%. We cannot use these data for modelling, because we need information about solar radiation and wind speed. So we have used climate data for Tehran from EnergyPlus and for Katrine (the nearest village), from Meteonorm. These data are interpolated from generally incomplete data sets. They miss some interesting local phenomena because they use general algorithms for interpolation.

The library climate is worth noting, because the new library should not be wildly different in climate. For example, applying BS5454, as the designer first considered, would be a form of climatic imperialism - enforcing a standard which is made for the northern European climate rather than for books in general.

[11] If we return to the basics of reaction kinetics. we can explain why the Sinai climate has preserved the library volumes so well. This is a Sebera type diagram in which the diagonal lines join points in temperature-RH space which have the same relative reaction rate, compared with 20C and 50% RH. This applies only to hydrolysis reactions, while oxidation certainly plays a part in paper and parchment deterioration. The high temperature in summer pushes the reaction rate up, but the corresponding very low RH pulls it back down again, to the standard rate at a European room temperature.

[12] Now we can wind the handle of the computer and predict the climate within the library, without any air conditioning. It's not bad at all. The temperature shows a smooth cycle from 12 to 30 degrees. The RH is more spiky but cycles from 27 to 40%. This is for a room with very little buffering - provided by cellular concrete cladding of the interior walls. As soon as some books are installed the RH will stabilise enormously, though the annual cycle will be the same, but smoother.

[13] But what about the pesky visitors? They breathe out water vapour and release heat. The water vapour does increase the RH by about 3%, when smoothed out over day and night.

[14] Here is a stretched version of the previous graph. The moisture release by visitors is clearly visible in this simulation, but it is not at all troublesome; indeed one could wish for a slight rise in RH in mid winter.

[15] Lest you think that these graphs represent an irresponsible relaxation of professional standards of care, here is the pre 1945 library, leaning up against the 6th century granite block wall. Above this wall is a medieval building up with granite boulders in earth mortar. Above that again is an earth wall. These raisings are evidence that Mohammed's letter was not totally effective. The walls had to be raised as better muskets allowed attackers to shoot down into the monastery from high in the surrounding mountains.