The effect of topical steroids on the aged human axilla, in Montagna V (ed): Advances in Biology of 8kin.#
I.

# RECOMMENDATIONS FOR AN ULTRAVIOLET RADIATION STANDARD
The National Institute for Occupational Safety and Health (NIOSH) recommends that occupational exposure to ultraviolet energy in the workplace be controlled by compliance with the following sections.
Ultraviolet radiation (ultraviolet energy) Is defined as that portion of the electromagnetic spectrum described by wavelengths from 200 to 400 nm. (For additional definitions and conversion factors, see Appendix II.) Adherence to the recommended standards will, it is believed, prevent occupational injury from ultraviolet radiation, that is, will prevent adverse acute and chronic cutaneous and ocular changes precipitated or aggravated by occupational exposure to ultraviolet radiation.
Sufficient technology exists to prevent adverse effects on workers, but technology to measure ultraviolet energy for compliance with the recommended standard is not now adequate, so work practices are recommended for control of exposure in cases where sufficient measurement or emission data are not available.
These criteria and the recommended standard will be reviewed and revised when relevant information warrants.

# Section 1 -Exposure Standards (a)
For the ultraviolet spectral region of 315 to 400 nm, total lrradiance incident on unprotected skin or eyes, based on either measurement data or on output data, shall not exceed 1.0 mW/cm^ for periods greater than 1000 seconds, and for exposure times of 1000 seconds or less the total radiant energy shall not exceed 1000 mW'sec/cm^ (1.0 J/cm^).

# (b)
For the ultraviolet spectral region of 200 to 315 nm, total lrradiance incident on unprotected skin or eyes, based on either measure ment data or on output data, shall not exceed levels described below.
Measurement techniques are discussed in Appendix I.
(1) If the ultraviolet energy is from a narrow-band or mono chromatic source, permissible dose levels for a daily 8-hour period can be read directly from Figure 1-1, or, for selected wavelengths, from (2) If the ultraviolet energy is from a broad-band source, the effective irradiance (I x ,) relative to a 270-nm monochromatic source exf shall be calculated from the formula below. From the permissible exposure time in seconds for unprotected skin or eyes shall be computed by dividing 0.003 J/cm , the permissible dose of 270-nm radiation, by I ,, in W/cm^. eff where I -effective irradiance relative to a monoe chromatic source at 270 nm. I  spectral irradiance in W/cm^/nm. A - relative spectral effectiveness (unitless); see Table 1-1 for values of at different wavelengths.
 band width in nm. If radiation intensity from a point source is known at some distance from the worker, for example, from measurement at another point or from output data at a known distance from the ultraviolet source, attenuation of radiation from that point to the worker can be calculated from the principle that radiation decreases with the square of the distance it must travel. For 1-2 example, an object 3 feet away from a radiation source receives 1/9 the energy of an object 1 foot away. This assumption is conservative
In some instances, since ultraviolet radiation, especially at very low wavelengths, may be absorbed by some components of the atmosphere.
Where information on atmospheric absorption of ultraviolet radiation is known, further correction may be applied. The calculation of intensity of radiation at any given point by use of the inverse square formula explained above does not take into consideration reflected energy.
The recommended standard is not proposed for application as a standard to lasers. It should be recognized that significant nonoccupatlonal exposure to ultraviolet radiation can occur from exposure to sunlight, particularly during the summer months.
(a) The worker's past medical history should be obtained to determine if the worker suffers from any condition that Is exacerbated or aggravated by exposure to sunlight. (b) A worker who gives a history of such a condition should not be permitted to work in an area exposed to ultraviolet radiation.
(c) The worker should be advised that any blemish that appears on skin exposed to long term ultraviolet radiation should be examined by a physician.

# Section 3 -Apprisal of Employees of Hazards From Exposure to
Ultraviolet Energy.
(a) Each employee who may be exposed to high Intensity artificial sources of ultraviolet energy shall be apprised of all hazards, relevant symptoms and precautions concerning exposure. This apprisal of hazards shall Include:
(1) Information as to the proper eye protection and protective clothing to be used.
(2) Instruction on how to recognize the symptoms of eye and skin damage due to ultraviolet radiation.
(3) Information as to special caution that shall be exercised in situations where employees are exposed to toxic agents and/or other stressful physical agents which may be present in addition to and simultaneously with ultraviolet radiation. All sources, work areas, and housings specified in
Worker exposure to ultraviolet energy from 200 to 400 nm shall be controlled by adherence to the standard set forth in Section 1 or the preventive procedures described in this Section, as applicable.
Compliance with the standard, based on measurement data or emission data, or adherence to the work practice procedures will protect against injury from ultraviolet energy.
Exposure to ultraviolet energy can be controlled by enclosures, shields, protective clothing, skin creams, gloves, goggles, or face shields.
Workers shall be protected from eye or skin exposure to ultraviolet radiation.
Specific protective measures to be used for various types of ultraviolet exposure are noted below. Additional hazards. There are other hazards from some ultraviolet sources that must also be prevented. There is a shock hazard in some operations involving arcs, because of the high starting voltages required;
wiring and connections must be adequately insulated, and persons handling the equipment must wear gloves and face shields. There must be adequate ventilation to prevent build-up of ozone and oxides of nitrogen. There may also be an explosion hazard from some ultraviolet operations, and the wearing of gloves and face shields will reduce the consequences of an explosion.
Arc welding on plates wet with unsaturated chlorinated hydrocarbons (perchloroethylene and trichloroethylene) must be avoided unless well vented, because of possible production of phosgene and hydrogen chloride.

# Section 6 -Recordkeeping
Because measurement of exposure of workers to ultraviolet energy Is not required, records are not required.

# Historical Reports
The light-induced, acute inflammatory reaction of the eye has been known since early times, as indicated by Xenophon's mention of "snowblindness" in his treatise Anabasis (ca. 375 BC), quoted by Duke-Elder.
Although more energetic than the visible portion of the electromagnetic III-l spectrum, most ultraviolet radiation is not detected by the visual receptors in mammals, including man. Thus, exposure to ultraviolet may result in ocular damage without the subject's being aware of the potential danger.
Cases of keratinization of the cornea and cataracts of the lens have been 2 3 observed since the early part of this century - from ultraviolet radiation levels associated with welding arcs, high-pressure pulsed lamps, and reflection of solar radiation from snow, desert and water.

# Effects on Humans
Reviews of the literature on the biologic effects of ultraviolet Ozone is produced principally at wavelengths less than 220 nm.

# Effects on eyes
Ordinary clinical photokeratitis has been described by Pitts and 9 Gibbons as characterized by a period of latency that tends to vary inversely with the severity of exposure. The latent period may be III-2 as short as 30 minutes or as long as 24 hours, but Is usually 6 to 12 hours. Conjunctivitis follows, often accompanied by erythema of the facial skin surrounding the eyelids. There is a sensation of a foreign body or "sand" in the eyes and varying degrees of photophobia, lacrlmation, and blepharospasm. These acute symptoms usually last from 6 to 24 hours with nearly all discomfort disappearing within 48 hours. The Individual is visually incapacitated for varying periods of time. It Is important to note that the ocular system, unlike the skin, does not develop tolerance 9 to repeated ultraviolet exposure.
Quantitative dose-response studies on eyes have been conducted in man and animals, and the two approaches have complemented each other; some of the following comments on effects on the human eye are amplified and compared with studies on animals in the section on Animal Toxicity.
Pitts and Tredici studied threshold intensities for production of photokeratitis. From animal studies, they predicted maximal sensitivity of humans to occur at 280 nm and exposed a few humans at this wavelength.
From the limited results, they estimated a threshold at 280 nm of to the difference in the absorption of the different wavebands. The lower wavebands were absorbed In the outer corneal epithelial layers and underwent rapid change whereas the higher wavebands were absorbed in the deeper epithelial layers and showed delayed changes because these cells were more viable. Thus, the response at shorter wavelengths was rapidly revised while at the longer wavelengths there was a delayed and more serious response.

# III-5
Through a series of graded determinations ranging from -to + +, the first + reaction is taken to be the MED.  Melanin, the pigment responsible for varying degrees of skin coloration, is present in the epidermis of the skin.^ When it is present in high concentrations, the deeper levels of the skin are protected from damaging effects of ultraviolet radiation, the melanin acting somewhat as a supplementary epidermal biological filter. The process of melanin pigmentation in the skin is believed to be initiated from pigment granules present in melanocytes with transfer of the granules Oil to neighboring cells in the basal layers of the skin.
The number of 07 melanocytes in Negro and Caucasian skin is about the same, so that differences in degree of skin pigmentation result from differences in cell activities. Longer wavelengths than those required for erythema produce some suntanning, even wavelengths extending well into the visible range.3
Miescher^O showed that the ratio of thresholds for mild sunburn was about 8 times as great for Negro skin as for Caucasian skin, and about 120 times as great for severe sunburn. Thus, though skin pigmentation does afford protection from sunburn, Fitzpatrick^1 III-7 demonstrated that erythema nevertheless does occur In deeply pigmented skin even though It is extremely difficult to measure.
The manner in which melanin affords protection is not entirely 42 understood. Daniels, in reviewing the relation between pigment and human adaptation to environmental radiation, stated that it was unlikely that a darkly pigmented skin was required solely as a shield against the ultraviolet radiation of sunlight.
The epidermis of the Bkln which has been exposed to mild doses of ultraviolet radiation becomes thickened, initially due to inter-and intra-cellular edema. After approximately 72 hours, the mitotic rate has accelerated and increased cellular production contributes to the epidermal thickening. All layers of the epidermis, except for the basal layer, are thickened and remain so with further stimulation. The thickened epidermal layer affords protection against damage by ultraviolet radiation. The potential protection afforded by the thickened epidermis is illustrated by the practical impossibility of eliciting an ultraviolet erythema in the palms of the hands or soles of the feet. Calculations based on the thickness of the horny layer have shown that a dose many thousandfold that of the MED for trunk skin would be required to produce erythema in such areas as the palms of the hands. a greater incidence of basal cell epithelioma and malignant melanoma than control groups. There was a 25 percent greater incidence of basal cell epithelioma among men than among women, most likely because men spend more hours outdoors for work or sport. Ninety-one percent of the basal cell epitheliomas were on sun-exposed parts.  MW sec/cm^ was given to two groups of albino mice. Tumors developed in

# Worthy of brief mention is
the group exposed to 300 nm radiation but not in the group exposed to 310 nm. Winklemann^ found that 280 nm to 310 nm induced squamous cell carcinoma in the skin of hairless mice.
Prior to 1960, sarcoma was the primary tumor produced experi-49 mentally by ultraviolet radiation on the ears of albino mice and rats.
With the development of hairless mice, squamous cell carcinomas were 97 reported and further studies established that squamous cell carcinomas could be produced almost to the exclusion of connective tissue (sarcoma) 96,98 growths.
The hairless mouse has also provided an experimental sodel for demonstrating that benign pigmented lesions could be stimulated 99 to develop into malignant melanomas by ultraviolet radiation. This further emphasizes that exposure to the sun may play an important role The dose of ultraviolet radiation necessary to give a threshold erythema reaction at 253.7 nm wavelength is only about 50% of that necessary at 300 nm.
A limit of 0.1 yw/cm^(8.6 mJ/cmfor 24 hours 104 has been established.
Again, the proposed minimum hazard level is satisfactory at the 254 nm wavelength (6.0 mJ/cm^).
The comparative photokeratitic thresholds for the cornea shown in Above 300 nm, a trend toward decreased sensitivity is noted and would be expected to be quite marked as seen in the rabbit. The photo- 1000 ^U/cm at 253.7 nm and 400 PW/cm at 365.0 nm. The sunburn was followed by desquamation and pigmentation.
Cases of dermatitis and erythema have been reported from ultraviolet radiation below 320 nm produced by fluorescent lamps used for general lighting purposes. Irradiance levels were not known.
IV.

# ENVIRONMENTAL DATA
Although there is much information on Industrial applications of ultraviolet energy, there is little information on exposure levels. The Both of these values are substantially below the "standard" action spectrum to protect against erythema.
Recognizing that many factors affect Individual responses^, MateJ-sky11^suggested, based on the "standard" erythema action curve, the following threshold doses weighted on the basis of their action spectra:
(1) Minimum erythemal dose for previously non-exposed skin: 9 20 to 25 mJ/cm of erythemally-weighted ultraviolet.
(2) Minimum erythemal dose for previously exposed skin: 2 25 to 35 mJ/cm of erythemally-weighted ultraviolet.
(3) Minimum keratitic dose;_ 1.5 mJ/cm ^ of keratitically-weighted ultraviolet.
The American Conference of Governmental Industrial Hygienists has proposed Threshold Limit Values, for 320 to 400 nm, of 1.0 J/cm2 for periods greater than, and 1.0 mW/m^ for periods less than, 1000 seconds.
For the actinic spectral region of 200 to 315 nm, the Conference proposed limits described by a curve (see Figure 1-1) In which the maximum permissible doses range upward at both longer and shorter wavelengths from 3.0 mJ/cm^ at 270 nm.

# Basis for Recommended Standard
The environmental exposure standard recommended in this document is the same as that proposed by the American Conference of Governmental 120 Industrial Hygienists. The ACGIH has not published the documentation or reasoning behind their proposed standard. The NIOSH rationale for recommending the same environmental exposure standard is as follows:
The results of the early investigators were quite consistent in the 280 to 315 nm range, but were somewhat divergent in the lower wavelengths action spectra.

# V-3
There has been little uniformity in the choice of body sites irradiated by the different Investigators. Olson, Sayre, and Everett1^ have shown the trunk to be more sensitive than either the head or the extremities, and the abdomen (used by them to develop their action spectrum^) the most sensitive of three trunk locations tested. After exposing abdominal skin to ultraviolet radiation at nine wavelengths between 250 and 310 nm, they reported that, while erythema response was well developed for all wavelengths after 8 hours, the response had substantially decreased at the shorter wavelengths after 24 hours. Furthermore, the energy requirements for minimal perceptible erythema at 254 and 280 nm were lowest at 8 hours after irradiation and nearly twice as much at 24 hours. The energy requirements for minimal perceptible erythema at 297 nm, however, decreased about 5% between 8 and 24 hours. Thus, it is apparent that the recent erythema action spectra, indicative of minimal perceptible erythema doses determined 8 hours after irradiation of a sensitive part of the body should at least reflect lower energy requirements and possibly other differences as well, when compared to the traditional curve.
Relatively minor damage to the conjunctiva or cornea from ultraviolet results in photophobia, pain, epiphora, and blepharospasm. Although the response is acute and incapacitating at the time, it regresses after several days leaving no permanent damage.The action spectrum for photokeratitis developed by Pitts and Tredici,10 based on animal and human data, is slightly more conservative than the recent skin erythema curves and reflects maximum efficiency at 270 nm rather than 250 nm. Nevertheless, this curve and the recent erythema action spectra are In reasonably good agreement. This is in keeping with previous statements that the action spectrum for conjunctivitis V-4 is the same as that for skin erythema. 8 Sllney compared the action spectra, both for erythema and for photokeratltls, with the "standard" erythema action curve. Plotting energy versus wavelength, the recent action spectra are at considerably lower energies than is the traditional curve. Additionally, these action Second, the curve is, as mentioned, almost flat. This is in contrast to the animal photokeratltic curves reported by Pitts and Tredici1^ and 9 again in the Pitts and Gibbons paper. While it may well be true that the human response varies slightly, if at all, with wavelength, the present results alone are not strong enough to support such a conclusion. Consequently, g the curve drawn by Sliney is believed not to be invalidated by the data of Pitts and Gibbons.
Assigning a relative spectral effectiveness of 1.0 to 270 nm, the low point of the recommended standard, the relative spectral effectiveness of other wavelengths can be calculated (Table 1- The recommended standard (Figure 1-1) is based upon action spectra both for erythema and for keratoconjunctivitis and is intended to protect the skin and eyes against acute effects. Therefore, separate skin and eye standards are not recommended. The American Conference of Governmental Industrial Hygienists proposed the limits expressed In this recommended standard and they specified its applicability for protection of both eyes and skin. The recommended standard is more readily applicable to the eye since the eye, unlike the skin, does not acquire protective capabilities after repeated exposures.
On the other hand, the skin does acquire resistance to ultraviolet damage after repeated exposure. Additionally, individual variations in threshold 119 response are great. Matelsky states that, despite the extensive industrial exposures to ultraviolet radiation, no cases of industriallyinduced skin cancer or keratosis have been reported and concludes that protection against the painful acute effects adequately V-7 protects ag3ixi8f tumorigenic doses. Nevertheless, It is believed that there Is not enough information to be completely sure that Industrial exposures to ultraviolet energy will not cause chronic effects on eyes or skin, such as cataracts or skin tumors.
While erythematic and carcinogenic activity is limited to wavelengths 33 90 119 shorter than 320 nm, ' - the lens of the eye absorbs strongly in the 300 to 400 nm range. "Black-lights" have a powerful emission line of 366.3 nm, which can cause the lens to fluoresce. This apparently causes some people, when looking at "black-lights", to experience a "tired" feeling, blurred vision, discomfort, and sometimes headache, but apparently no permanent damage ensues.
There is some evidence from animal studies to implicate ultraviolet in 81 this range as contributing to cataract formation.
While few industrial sources emit strongly in this range, the standard for 320 to 400 nm is recommended to prevent occupational exposures in this range from exceeding levels normally encountered in the out-of-doors.
Normal individuals should be adequately protected by these standards.
Photosensitive individuals, however, may respond at extremely low energy levels and over very wide wavelength ranges, even into the visible w av e le n gth s.^22 Therefore, these standards may not be adequate for photosensitive Individuals. More research is needed before the adequacy of these standards in protecting against chronic effects on skin and eyes can be assured.
V-8

# VI. PROTECTION AND CONTROL MEASURES
Skin and eyes can be protected from the effects of ultraviolet radiation by shielding of sources of radiation, by goggles or face shields, by clothing, and, for special purposes, by absorbing or reflecting skin creams.
Principles and procedures in selecting suitable protection are summarized in this section, and studies of various protective measures are reviewed. Specific topics discussed are (1) sunscreens, (2) pro tective clothing and barrier creams, (3) transparent material for skin and eye protection and (4) reflection of ultraviolet radiation.
(1) Sunscreens
Sunscreening preparations are usually classified as chemical or physical. The former Include para-aminobenzoic acid and its esters, cinnamate8, and benzophenones, all of which act by absorbing radiation so that the energy can be dissipated as radiation of lower energy. The physical agents act as simple physical barriers, reflecting, blocking, or scattering light. They include titanium dioxide, talc, and zinc oxide.
Largely because of cosmetic objections, the physical barriers are infrequently used In sunscreen formulations.
Sunscreen protection from absorbing chemicals depends on maintenance 127 of film thickness. Robertson reported that a series of sunscreens of 0.0 1 mm thickness protected fair skin during four to five hours of sunshine if the protective layer was fully maintained for the whole period.
When the thickness of the layer was halved, erythema occurred within a maximum of one hour.

# VI-1
Pathak, Fitzpatrick and Frenk produced evidence suggesting that para-aminobenzoic acid and its esters in ethanol afforded protection against the sunburn range (290 to 320 nm) for several hours with one application and that the protective action was unaffected by bathing, swimming, or vigorous exercise. MacLeod and Frain-Bell1^ confirmed the effectiveness of para-aminobenzoic acid in ethanol and observed that protection was provided for up to seven hours after the initial application.
They found, however, that the agent was easily removed as a result of 130 bathing or exercising. Katz also noted that para-aminobenzoic acid is not water-resistant; he found that a consistently satisfactory protection against the erythematogenic rays of the sun was lost after a 10-minute swim.
Goldman and E p s t e i n -^l reported that a commercial sunscreening agent containing the ultraviolet-absorbing chemical glyceryl para-aminobenzoate was a photosensitizer and that it had produced severe dermatitis in a patient who applied it prior to exposure to sunlight. The agent was an ordinary contact allergen as well as a photosensitizer. Turner, Barnes and Greene-32 found that a preparation containing vitamin A and calcium carbonate reduced the unpleasant effects of solar radiation without affecting normal tanning. The beneficial effect was most marked in subjects with blond hair. This observation could not be repeated, according to Findlay.^3
Red veterinary petrolatum is cosmetically less acceptable than other agents, but has a long history of effective protection of normal skin from the damaging effects of the ultraviolet sunburn spectrum. Like the benzophenones, it also gives some protection in the long ultraviolet doubted Its efficacy with their patients.
For Individuals with chronic photosensitivity diseases, It Is desirable to add a light-scattering and reflecting agent (e.g., titanium dioxide, talc, and zinc oxide) In combination with a light absorber in a hydrophilic ointment.
(2) Clothing and Barrier Creams Protective clothing consists of long-sleeved garments to protect the arms while a small cape sewed to the cap protects the back of the neck and the sides of the face. Flannelette and poplin give maximum protection, while other materials give less protection (Table X -4).
Where it is impossible to shield the skin by clothing, polyvinyl chloride gloves, masks, shields or by redirecting the radiation by suitable reflectors, a barrier cream should be applied to the skin before Irradiation. Ordinary soft paraffin is an excellent barrier, but its greasiness will often preclude its use on hands. Barrier creams contain ingredients which absorb ultraviolet radiation. The benzophenones are the best compounds for this purpose because of their great absorption capability 139 throughout most of the near and far ultraviolet spectrum (Parrish et al.
VI-3 As can be seen from the curve, the transmission falls off rapidly with wavelength below 360 nm.
Window glass 1/8 In. in thickness is adequate protection for the eyes and skin against ultraviolet radiation from ordinary ultraviolet sources. In the case of very intense sources of ultraviolet radiation, It may not be sufficient.

# VI-4
Full protection against 253. Glass workers, arc welders and people engaged In similar types of work may be exposed to infrared radiation as well as ultraviolet radiation, and may need eye protection from both types of radiation. Such people should wear goggles with an infrared absorbing glass and an infrared reflecting surface. Ordinary glass, plastics and other materials are usually transparent to Infrared rays which can cause thermal damage to the eye. A glass that absorbs in both the ultraviolet and infrared regions of the spectrum will be needed in such cases. For listings of absorbing 142 glasses refer to ANSI-Z 49.1.

# (4) Reflection of Ultraviolet Radiation
When a number of ultraviolet generators are operating in one room, protection of personnel poses several problems. In many applications, little difficulty is encountered in properly shielding the source so that most, or all, of the output is restricted to the exposed material. Stray radiation can be reduced, but reflection from glass, polished metal, and VI-5 high-gloss ceramic surfaces can be harmful to people working In the room.
Absorption of ultraviolet radiation therefore becomes an Important Item to consider In planning a safe work environment. Since painted walls and ceilings can be a significant source of ultraviolet reflection, It Is necessary to consider the ultraviolet reflective properties of the paint used.
The reflection of Incident ultraviolet radiation from pigments can range from negligible to more than 90%. A given material's ability to reflect visible light is no indication of its ability to perform similarly with ultraviolet. Table X-7 gives the reflection from a number of white pigments and other materials at several wavelengths In the ultra violet. The table shows that ordinary white wall plaster has a reflection of 46% at 253.7 nm, whereas zinc and titanium oxides, which are equally good reflectors for visible light, reflect only 2.5% and 6%, respectively, at this wavelength. 0 11-vehicle paints usually have low reflectances because of the absorption by the oil. However, some paints using synthetic plastic vehicles with high ultraviolet transmission may have high reflectances.
Walls surfaced with gypsum products tend to have high reflectances.
Table X-8 shows the ultraviolet reflectance of a number of dry white pigments in the region between 280 and 320 nm. These measurements were made with the unresolved radiation from a S-l lamp as a source and a cadmium phototube as a detector. These measurements may be assumed to be predominantly at the wavelength 302.4 nm.

# VI-6
No assumptions regarding the reflections of white pigments should be made without investigating their composition. The reason for this is demonstrated by the difference between two white pigments, zinc oxide and white lead. Although both of the pigments are very good reflectors of visible radiation, zinc oxide reflects only 3% of the ultraviolet, whereas white lead reflects about 60%. Colored pigments are almost invariably poor reflectors of ultraviolet. Stutz1^ studied 38 colored pigments and found that only turquoise blue had a reflectance of as much as 25% at 331.1 nm. At 253.6 nm turquoise blue had a reflectance of 22%, whereas none of the others exceeded 7.5%.
Table X-9 shows the ultraviolet reflectance of a number of paints with different white pigments suspended in silicone.
The basic requirements which determine the reflecting power of an 141 ultraviolet-reflecting paint have been given by Roller :
1. Particles of the pigment must be low in absorption (except metallic pigments), so that a large portion of the Incident radiation Is returned by multiple reflection and refractions.
2. The binder or vehicle must be transparent to the radiation to be reflected.
3. The difference in refractive index between pigment and medium must be large so that reflection and refraction at pigment-medium interfaces will be appreciable. the availability of measuring devices to cover these specific areas of the ultraviolet spectrum.
The band between 320 to 280 nm is referred to as the erythemal region with 295 to 298 nm being the wavelengths of maximal effect.
This area is also the one which has been Identified as having a carcinogenic effect upon the skin.
Slightly overlapping these wavelengths is a germicidal band between 280 and 220 nm with a maximum germicidal effective wavelength at 265 nm with some erythemal effect noted between 250 and 260 nm. In order to avoid errors of major magnitude In assessing ultraviolet energy, the following must be given serious consideration:
1. The spectral output of the specific source being evaluated and the spectral response of the phosphor or phototube that Is being utilized in measurement of ultraviolet energy. The selection of a meter or phototube should be one that is sensitive in the range most nearly covering that part of the spectrum under consideration.
Response curves of various phototubes are shown in Figure X-9.
2. Solarlzation and aging of lenses, tube envelopes, or cells.
This can be accomplished only by calibration against a source of known wavelengths and intensity.
3. Water vapor in the atmosphere may cause absorption of ultraviolet energy as well as affecting the electronic circuitry. There are several sources of commercial measuring devices available. These devices are primarily designed to measure output from specific sources. They are not in frequency ranges that can be satisfactorily utilized for purposes of evaluating exposures from wide band sources. An attempt to use these measuring devices with specific phototubes or phosphors can be extremely hazardous and give erroneous results when attempts are made to utilize them for wide-band ultraviolet energy.
Most of the devices are marketed as being sensitive at a specific wavelength. However, it should be pointed out that the ultraviolet response may be much wider than the one wavelength indicated; and the relative spectral response of each filter or phototube must be known to reasonably assess the exposure to ultraviolet energy. Examples of spectral response of several phototubes and filters are included in Figures X-9, X-10 and X-ll.
An ultraviolet device to measure broad-band ultraviolet energy is not presently available. However, it is possible to construct through a series of filters and phototubes a reasonable assessment of the levels of ultraviolet energy to which a worker may be exposed.