Because I have been asked about this subject several times, and because there will be a need for this information after a nuclear war, and because there does not appear to be anywhere that I can find a document on this subject - I have decided to write up this material myself. For any who may decry my lack of expertise in this area, I will certainly accept their reservations and only ask that they provide me with a better article for posting.

Matthew24:22
And except those days should be shortened,
there should no flesh be saved:
but for the elect's sake those days shall be shortened.

UVC is almost completely absorbed by ozone and oxygen in the atmosphere; even with severe ozone reduction UVC would still be effectively absorbed by the remaining oxygen.

UV is one of the non-ionizing radiations in the electromagnetic spectrum and lies within the range of wavelengths 100 nm (which corresponds to a photon energy of approximately 12 eV) to 400 nm. The short wavelength limit of the UV region is often taken as the boundary between the ionizing radiation spectrum (wavelengths < 100 nm) and the non-ionizing radiation spectrum.

UV of wavelengths less than 180 nm has no direct biological effect on humans since it is effectively absorbed in a few centimetres of air.

NOAA/National Weather Service
National Centers for Environmental Prediction
Camp Springs, MD 20746

The conversion from Erythemal Dose rate to UV Index is as follows:

an Erythemal Dose Rate of 25 milliWatts/sq meter equals 1 UV Index unit.

For instruments that output in MEDs the common conversion is this:


1 MED per hour equals 58 milliWatts/sq meter equals 2.3 UV Index units.

If you have questions about health aspects contact the U.S. EPA at 1-800-296-1996. If you have questions about scientific aspects contact the NWS at (301) 713-0622.

Of the two useful means of measurement of the intensity of UV described above the second appears most practical for our use and is calibrated in a unit called a MED.

An MED is the radiant exposure of UV that produces a just noticeable erythema on a previously unexposed skin. 200 - 300 J m-2 effective is the value of 1 MED.

LAT	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0	12	14	14	12	11	11	12	13	15	13	12	12
5	11	13	13	13	12	12	12	13	14	12	11	11
10	11	12	12	13	12	12	13	14	13	12	11	9
15	8	11	11	12	12	12	13	13	12	11	8	7
20	7	10	10	12	13	13	13	12	11	10	7	6
25	5	7	9	10	11	12	12	11	10	8	5	5
30	4	6	8	10	10	12	11	10	10	6	5	3
35	2	4	6	8	9	10	10	9	8	5	3	2
40	2	3	5	8	8	10	9	9	7	4	2	1
45	1	2	4	6	7	9	8	7	5	2	1	1
50	1	1	3	5	6	8	8	6	4	2	1	0
55	0	1	2	4	5	7	6	4	3	1	0	0
60	0	1	1	3	4	6	5	4	2	1	0	0
65	0	0	1	2	3	5	4	2	1	0	0	0
70	0	0	1	1	3	4	3	2	1	0	0	0
75	0	0	0	1	2	3	2	1	0	0	0	0
80	0	0	0	1	1	2	1	1	0	0	0	0
85	0	0	0	0	1	1	1	0	0	0	0	0
90	0	0	0	0	1	1	1	0	0	0	0	0

Outdoors, exposure to UV constantly changes during the day. People are largely unaware of the degree of these changes. At noon, when the sun is overhead, the level of UV at a wavelength of 300 nm is ten times greater than at either three hours before (9 am) or three hours after noon (3 pm). An untanned person with fair skin may receive a mild sunburn in as little as 25 minutes at noon (depending on the time of year and the latitude) but would have to lie in the sun for at least two hours to receive the same dose after 3 pm. The global biologically effective UV falling on a horizontal surface occurs primarily during the midday hours, about 50% during the four hours centred on noon-time zenith (Sliney, 1987).

Increased levels of UV due to ozone layer depletion may have serious consequences for living organisms. A 10% reduction in ozone could lead to as much as a 15-20% increase in UV exposure depending on the biological process being considered.

Snow, sand and water are all reflective surfaces and will intensify UV exposure to varying degrees. Grass reflects from 2.5 to 3 percent, sand reflects 20 to 30 percent, snow and ice 80 to 90 percent. Depending on the angle of reflection, water can reflect up to 100 percent of rays striking the surface.

Speculation as to how much UV may be presented or present is largely useless. What will be needed is a reliable method of measure. We shall examine both methods of measure and methods of defense in later sections, but first let us look at the effects of intensified UV.

The production of phytoplankton has been estimated at about 6 x 1014 kg (UNEP, 1989). A loss of 10% would far exceed the gross national product of all countries in the world, assuming any reasonable price for biomass on the market.

Field and laboratory experiments on plant responses to increased UVB radiation underscore the concern for agriculture, forestry and natural ecosystems as the stratospheric ozone level is depleted. Growth and photosynthesis of certain crop plants can be inhibited even under ambient levels of UVB radiation. Certain environmental factors, both biotic (e.g. plant diseases and competition with other plants) and abiotic (e.g. carbon dioxide, temperature, heavy metals, and water availability) can alter UVB effects in plants. This increases the difficulty in making any quantitative predictions. Plants in temperate regions and certain tropical species were found to be adversely affected by enhanced UVB radiation. Marine ecosystem which provides the primary food for human consumption (in some countries) has been shown to be more sensitive to UVB than terrestrial plants. One consequence of loss in phytoplankton is reduced biomass production which would be propagated throughout the whole food web. The marine phytoplankton is a major absorber of atmospheric carbon dioxide. Any reduction in this population would decrease the uptake of carbon dioxide and so augment the greenhouse effect.

Some amounts of UV are beneficial in the same way that some amounts of arsenic are beneficial (in fact necessary).

For the entire system of vitamin D3 production the amount of UV radiation reaching the skin is critical. The doses needed are small, and daily exposures of the face and hands to sun and light for 15 minutes is considered sufficient. The minimum dose requirement was estimated to be equivalent to 55 MED per year (Health Council of the Netherlands, 1986). When too little UVB reaches the skin, deficiencies of vitamin D may occur, resulting in a weakening of the bones. Groups at risk are particularly dark-skinned children in high latitude cities and elderly people living entirely indoors. Supplementation of vitamin D3 in the diet is then recommended.

It has (also) been suggested that beneficial effects of UV exposures may occur such as: improvement of cardiopathy and functions, and better microorganism defense.

One beneficial effect of modest exposure to UVB radiation is the maintenance of the ability of the skin (through sun tanning) to sustain further UV exposures. Loss of this adaptation forms an important component in photodermatosis, skin diseases where the lesions are caused by light. These patients can be treated by regular exposures to UVB. The doses required are in the same range as that needed for the synthesis of vitamin D3.

The criteria that I have established for selecting proper instrumentation is as follows:

1. is not prohibitively expensive

2. is not overly complicated and directed towards scientific uses

3. is not difficult to maintain and calibrate

4. is not too simplistic so that it will give us a meaningful scale

5. is not too limited in its scale so that it may not respond to the high ranges about which we are speculating as to occurriing

6. is hardened so that will not be damaged by those high ranges

7. is not overly delicate so that we can use it in the hazardous situation that we anticipate

8. ideally the equipment would be either EMP hardened or not EMP sensitive, however there are other solutions for dealing with EMP.

Eye protection is extremely important. Long term effects in the way of eye cancer and blindness can be very detrimental.

For outdoor workers and the general public, the most hazardous source of UV exposure is the sun. Adequately designed (ski) goggles afford protection against exposure to solar UV at high altitudes and on snow, but for most other exposure conditions, good UV absorbing sunglasses (under normal conditions) are an adequate means of eye protection.

If dark lenses are placed over the eyes, the natural aversion to bright light, which leads to the squint reflex (that greatly lowers retinal UV or exposure to the eye), would be disabled. This may appear to be an unusual way to consider the comfort that shaded lenses provide. However, poor sunglasses may actually lead to a higher UV exposure (Sliney, 1983).

Face shields, goggles or safety spectacles which absorb UV should be worn where there is a potential eye hazard.

People seldom look directly at the sun when it is overhead and very hazardous to view. It is not very hazardous to view when the sun is low in the sky and falls within the normal field-of-view. When the sun is more than 10� above the horizon, the natural tendency is to partially close the eyelids or squint (called squint reflex), thus shielding the retina from direct exposure. These factors reduce the exposure to the cornea to a maximum of about 5% of that falling upon the exposed top of head (Sliney, 1986). If the squint and other behavioural factors are not considered, the dose to the eyelid would be approximately 20% of the dose falling on a horizontal surface.

When looking at snow, UV is reflected directly into the eye; hence, the traditional eye protector of the Inuit or Eskimo, the slit, in whalebone or in a seal-skin mask, provided geometrical rather than spectral protection against UV exposure (Hedblom, 1961). The lack of protection above and to the sides of sunglasses is a serious shortcoming. However, to obtain a quantitative idea of this component of exposure to the eye, measurements were made using a simulated ocular geometry in sunlight (Sliney, 1986). The human eye received 10 to 25 % of the UV dose when wearing glasses with lenses opaque to UV compared to no lens in the glasses. Therefore, unless goggles with side-shields are used, UV transmission factors in lenses much less than 2-5 % do not provide the eye protection suggested by the transmission factor (Sliney, 1986).

Nutrition can provide the body with essential antioxidants and these molecules are distributed throughout the body. At the cellular level, they enter a number of endogenous photoprotective systems to control photochemical processes (Roberts et al., 1991). Quenchers which can negate specific reactive intermediates may be important as a defence mechanism against UV insult to the eye. Glutathione, due to the low energy of the SH (thiol) bond (65 kcal) is an efficient free-radical scavenger and singlet oxygen quencher. Ascorbic acid quenches free radical and superoxide reactions. alpha-Tocopherol quenches both singlet oxygen and free radicals. There are also various antioxidant enzymes present in the eye. Exogenous scavengers and quenchers may be able to prevent UV damage by interrupting transient intermediates which cause ocular damage. An approach is to increase the known endogenous quenchers, (antioxidants) ascorbic acid, alpha-tocopherol and �-carotene in the diet (Roberts et al., 1991).

Surprisingly, while millions of dollars are spent marketing sunscreens and the pharmaceutical companies, medical associations, and weather bureaus all combine to promote them, the scientific studies themselves indicate that they are contra-indicated. That is to say - you should not use them. The reason is - UVB darkens the upper layers of the skin, and the creams and lotions enhance this darkening so that one does not as readily burn if they develop a tan (and some tanning is beneficial for that reason). HOWEVER, the tan does not prevent the UVA from penetrating through to the deeper cells where the DNA is affected and the detrimental causes of cancer occur. For this reason sunlamps and sun tanning are generally non-beneficial.

Here the protection factor is an estimate of the protection afforded against biologically effective solar radiation. A statistically significant positive association of "often or very often" use of sun protection agents with melanoma (relative risk 1.8, 95% confidence interval 1.5-3.8) was found by Beitner et al. (1990). In their cohort study of basal cell carcinoma in US nurses, Hunter et al. (1990) found a higher risk in those who spent 8+ hours per week outside and used sunscreen than in those who spent the same time outside but did not use sunscreen.

Sunscreens effectively block solar UVB. UVB is the normal stimulus for accommodation of the skin such as thickening and increased pigmentation. Sunscreens suppress normal warnings of overexposure such as erythema and sunburn and allow excessive exposure to wavelengths of sunlight they do not block. Due to lack of these natural signs sunscreens create a false sense of security and individuals tend to stay in sun longer. In view of these behavioural changes which increases individuals UVA exposure it has been suggested that, because of the rising incidence of melanoma, UVA may be associated with its occurrence (Garland et al., 1992). While a recent study (Setlow et al., 1993) in fish reported melanoma induction by UVA, the role of UVA in the causation of human malignant melanoma has yet to be established.

While further studies are still needed to clarify concerns raised about the ingredients and protectiveness of sunscreens, broad spectrum sunscreens which absorb both UVA and UVB with an SPF of at least 15 are still recommended as an effective means of personal protection against UV exposure.

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