Earth Science Exit Project

[Harley Scarow]

ULTRAVIOLET RADIATION

INTRODUCTION




This chapter may serve as a guide to industrial hygienists who

are responsible for evaluating and making recommendations for

the protection of workers from potential health effects of ultra-

violet radiation.




The guidelines and the exposure limits are based on available

knowledge and scientific research. The limits should provide a

healthy work environment for a majority of workers regarding

ultraviolet radiation exposure.




PHYSICAL PROPERTIES

Physics

Radiation is energy in transit. Electromagnetic radiation is made

up of oscillating electric and magnetic fields which are propagated

in free space and in matter. Collectively, the electromagnetic

spectrum includes: radiofrequency (radio, television and

microwave transmission); infrared, visible and ultraviolet light; X

and gamma radiations. Ultraviolet (UV) is part of the

electromagnetic radiation spectrum with wavelengths from

approximately 180 nanometers (nm) to 400 nm.




Electromagnetic radiation may be classified by properties such as

wave velocities, frequency or wavelength. These three

parameters of electromagnetic radiation are related by the

following:




c = ëv Equation (1)

where c = velocity (light in vacuum) a constant 3 x 108 meters

per second (m s-1)

ë = wavelength, distance occupied by one wave

(expressed in units of length such as meters,

micrometers, nanometers)

v = frequency, number of oscillations per unit time

(expressed as oscillations per second; the unit

Hertz (Hz))




The electromagnetic spectrum may be represented by either

frequency or wavelength as depicted in Figure (1). All

electromagnetic radiation, regardless of the medium, will exhibit

certain attributes such as reflection, refraction and diffraction.




Reflection takes place at an interface of materials. Two types of

reflection occur, specular (mirror-like) and diffuse. Surfaces with

irregularities or roughness produce diffuse reflections.

FIGURE 1

Frequency Wavelength

in Hz in meters

100 (1 Hz) 3 108

101 3 107

102 3 106 } Commercial Electrical

103 (1 KHz) 3 105 Power

104 3 104

105 3 103 (3 Km)

106 (1 MHz) 3 102 } AM Broadcast (535-1600

107 3 101 KHz)

108 3 100 (3 m) } FM Broadcast

109 (1 GHz) 3 10-1

1010 3 10-2 (3 cm)

1011 3 10-3 (3 mm)

1012 3 10-4

1013 3 10-5 ┐

1014 3 10-6 (3 um) ┘ Infrared

1015 3 10-7 } Visible Light

1016 3 10-8 ┐

1017 3 10-9 (3 nm) │ Ultraviolet

1018 3 10-10 ┘

1019 3 10-11 │

1020 3 10-12 │ X Rays[/td][/tr][/table]




Diffuse and secular reflections are wavelength dependent. A

surface may produce a specular reflection at one wavelength but

diffuse at another (due to the size of the surface roughness in

relationship with the wavelength).




Refraction takes place at an interface when a beam passes from

one media to another having a different refractive index. It is

responsible for the bending of the light near air-water, air-glass

interfaces. Lenses and prisms are optical methods that use the

principle of refraction.




Diffraction of electromagnetic radiation occurs when waves pass

around an object in their path and are deflected. This may occur

when radiation passes through very narrow slits or small

apertures.




When radiation is transmitted through a material, it may lose

energy to the medium by various processes (absorption). In a

homogeneous material, the proportion of energy loss per unit

length is constant.




Ultraviolet radiation is usually divided into several ranges based

on physiologic effects:

UVA (near UV) 315 - 400 nm UVB (middle UV) 280 - 315 nm UVC (far UV) 180 - 280 nm

Radiations with wavelengths from 10 nm to 180 nm are

sometimes referred to as vacuum or extreme UV. These

radiations propagate only in a vacuum and thus biological studies

are of little value.




Some important absorption properties of UV radiations are as

follows:

UVA radiation is easily transmitted through air and glass. There

is penetration through the epidermis and the anterior ocular

media.

UVB and UVC radiation is transmitted through air and through

quartz but absorbed by ordinary glass. Absorption of these

wavelengths by the ozone layer of the upper atmosphere is the

reason why solar radiation on the earth's surface is almost

devoid of wavelengths below 320 nm. UV radiation below 315

nm is primarily absorbed by the cornea or the top epithelial skin

layer.




UV radiation with wavelengths below 200 nm is not easily

transmitted through air and usually exists only in a vacuum.




Of all the terms used to describe UV radiation, the

power or energy per unit area, irradiance (E) and radiant

exposure (H) respectively, are the most used. Irradiance (a dose

rate used in photobiology) is described in watts (unit of power)

per square meter (W m-2) or watts per square centimeter (W cm-

2). Radiant exposure (H), is dose, and is described in joules (unit

of energy) per square meter (J m-2) or joules per square

centimeter (J cm-2). Note that a watt is a joule per second thus

the dose rate (W cm-2) multiplied by the exposure duration

(seconds) equals dose

(J cm-2).




BIOLOGICAL EFFECTS

The absorption of UV radiation can cause biological effects. The

two primary organs of concern are the eye and the skin.




The UV spectral band of UVA (315-400 nm) is less

photobiologically active than the rest of the ultraviolet; UVB (280-

315 nm) and UVC (180-280 nm).




The adverse effects of UV radiation have been shown to be a

result of photochemical reactions rather than thermal damage.

This is shown by the rapid drop off of effects in the longer

wavelengths of the UV spectrum. The effectiveness of the

various wavelengths of UV radiation to produce a biological

response is referred to as an action spectrum. The maximum

sensitivity of the human eye was found to be at approximately

270 nm and this wavelength is used as a reference for

effectiveness of other UV wavelengths to elicit a biological

response. The relative spectral effectiveness is the ability to

produce a biological effect as compared to UV radiation at 270 nm.




Acute Effects

1. Erythema is a response to excessive exposure by UVB and

UVC radiation. The dose required to produce erythema varies

with skin pigmentation and the thickness of the horny layer

(stratum corneum). There may be a latent period of 4-8 hours

between the exposure and the symptoms. Symptoms may range

from simple skin reddening to serious burns. Darkening of the

skin and thickening of the stratum corneum offers some p

protection against future exposures. Erythema production is

dependent only on the total radiant exposure dose (product of

irradiance and exposure duration).




2. Skin photosensitization may occur when materials of

photosensitizing capabilities (pitch, petroleum products, coal tar

derivatives and some dyes or plants) are in contact with the skin

during UV radiation exposure. Sometimes, photosensitizing

substances are present as a result of a disease such as Lupus

erythematosus, Xeroderma and Herpes simplex.




Some therapeutic, diagnostic or cosmetic materials may elicit a

response when present in the body or on the skin during UV

radiation exposure. Some include chlorpromazines, sulfanilamide,

tetracylines, salicylates, anti-bacteriostatic agents such as

hexachlorophene, fungicides and oral contraceptives.




3. Acute kerato-conjunctivitis is an inflammation of the cornea

and conjunctiva after excessive exposure to UVB or UVC

radiation. This is also known as snow blindness or welder's

flash. Although the injury is extremely painful, it is usually

temporary because of the recuperative powers of the epithelial

layer. The latent period is usually 4-12 hours from the time of

exposure and is spectral and dose dependent. There is a

sensation of "sand" in the eyes, photophobia, blurred vision,

lacrimation and blepharospasm (painful uncontrolled excessive

blinking). Symptoms may last up to 24 hours with the corneal

pain being severe. Recovery takes one to two days.




The action spectrum and the threshold dose to cause kerato-

conjunctivitis has been investigated. The peak of the action

spectrum is 265-275 nm with the threshold for symptoms at

approximately 4 mJ cm-2.




UV industrial sources (welding or germicidal lamps) may

circumvent the natural defenses of the body and allow direct

exposure to the cornea. This occurs when the sources emit UV

radiation at angles unshielded by brow or eyelids.




4. The lens of the eye has about the same sensitivity to UV as

the cornea. The cornea however, is an efficient filter for UVC.

The cornea allows substantial transmission of UVA while the lens

has greater absorption (350-380 nm). The actual impact of UV

radiation exposure on the lens and causative effect (such as

cataract formation or photodegradation) is, at best, speculative

at this time. Arguments in favor of such effects are only

supported by exposures to experimental animals at very high

doses.




Chronic Effects

1. Skin aging may occur prematurely in individuals exposed to UV

radiation (UVB) for periods of many years. The skin appears as

toughened, darkened and wrinkled especially in outdoor workers

and has been referred to as "Farmer's skin."




2. Certain types of skin cancer may be induced due to exposure

to UV radiation. It appears in individuals whose skin is exposed

to solar radiation for a significant period of time (years). UVB has

been implicated as a cause of this effect.




Other Effects

1. Exposure to some UV radiation is beneficial where a type of

skin steroid (7-dehydrocholesterol) is converted to a form of

vitamin D (an intermediate in cholesterol biosynthesis).




2. UV radiation may interact with airborne compounds and

produce harmful substances. UVC radiation below 240 nm

interacts with oxygen (O2) and may form ozone (O3) or oxides of

nitrogen (NOX) in the atmosphere. The conversion of

hydrocarbons to oxidants may occur and is the main cause of

smog formations. UV radiation may also convert chlorinated

hydrocarbons to phosgene.




SOURCES

Sources of radiation can be grouped by the manner in which the

radiation is originated. When the temperature of some material

is elevated, many energy transitions occur and energy is emitted.




A main source of UV radiation on the earth comes from the sun.

However, when materials are heated to incandescence, some UV

radiation may be emitted. The spectrum (wavelengths) emitted

and the intensity is related to the temperature (absolute °K) of

the material. Therefore, open arcs, fluorescent sources and

incandescent sources can produce UV radiation with a wide

variation of wavelengths. Depending on the source, the radiation

emitted can be a broad band (so many wavelengths that it

appears as a continuum) or narrow, specific wavelengths (i.e. line

spectra from low pressure discharge lamps). The emitted

spectrum is an important factor in evaluating the radiation.




Lasers have been developed which emit UV radiation. Lasers

have specific characteristics which must be taken into

consideration for adequate evaluation. This chapter does not

address laser sources.




Besides the secondary production of UV radiation from arc and

incandescent sources, specific lamps are manufactured to

produce UV radiation in narrow spectral lines for germicidal

control. These are usually low pressure mercury vapor sources

that emit visible and UV wavelengths with 95% of the energy at

253.7 nm.




Some general lamp types are:

Incandescent Lamps, other than quartz-halide lamps normally

have glass envelopes to keep UV radiation from being a hazard.




Low-Pressure Discharge Lamps if they have quartz envelopes

may transmit UV radiation and may be of concern. Mercury low-

pressure lamps can create a severe UV hazard.




Fluorescent lamps usually have glass envelopes and may only

present a UV hazard theoretically at the surface.




High intensity discharge (HID) lamps may present UV hazards. If

the envelope is glass, there may be only a concern for UV

exposure at close distances. However, Quartz-Mercury HID

lamps require UV hazard evaluation.




Short arc lamps may produce a potential UV hazard because of

the temperature of the arc and the quartz envelope.




Carbon arc lamps may produce a potential exposure as with the

short arc lamps. This is compounded when no glass lens or filter

is present (a common situation).




HAZARD ASSESSMENT AND STANDARDS

If enough information can be obtained, numerous measurements

or calculations may be avoided. The following steps should be

taken to evaluate any UV light source:




1. Determine the Lamp Type - Categorizing the lamp can be

useful to determine the potential UV hazard.




2. Review the lamp manufacturer's data on radiometric

specifications. This can be of great value to determine the

hazard potential. Such data can be compared with data from

sources previously measured. Spectral data is the most useful.




3. Perform measurements when necessary if the above

information is incomplete or lacking (see the Evaluation Section).




4. Apply measurement results to the exposure limits.

The critical organs for UV exposure are the eye and skin. The

thresholds for the observed effects vary significantly with

wavelength. Therefore, "action spectra" have been developed to

create a dose response relationship. Basically, the "action

spectrum" refers to the relative spectral effectiveness of different

wavelengths to elicit a biological effect. Because some biological

effects to the eyes and skin vary with wavelength, human

exposure guidelines may be generated to express the efficacy of

the UV spectrum normalized to the most effective wavelength

(270-280 nm for the eyes). Acceptable exposure limits are based

on an action spectrum that combines the spectra for erythema of

caucasian skin with photokeratitis (eye). The result is a smooth

curve forming an acceptable criteria.




The limiting value of 3.0 mJ cm-2 (30 J m-2) is based on 270 nm

wavelength, where the eye appears to show the maximum

sensitivity for acute effects on the cornea. A safety factor of 1.5

to 2 is applied for acute photokeratitis.




Because the eye becomes more insensitive at other wavelengths,

the exposure limits change (increase) due to the fact that it takes

increasingly more UV exposure to elicit the same effects.




There has been much work to produce a basis to define a unified

action spectrum or a single curve to use for occupational

exposure evaluation which would apply for both the erythemic

and keratotic effects, yet be simple enough for the available field

instrumentation.




The National Institute for Occupational Safety and Health (NIOSH)

published a recommended exposure limit (REL) for occupational

exposure to UV radiation. The American Conference of

Governmental Industrial Hygienists (ACGIH) has also produced a

Threshold Limit Value (TLV®) for UV radiation very similar to

NIOSH. The protection limits are wavelength dependent in the

spectral region of interest (200-315 nm) and are based on the

action spectrum from thresholds of harmful effects in both animal

and human studies. The relative spectral effectiveness values

are basically a hazard weighting function. The action spectrum

curve is presented in Figure 2. Proper use of the limits requires

that the spectral irradiance of the source (Eλ) be multiplied

by the relative spectral effectiveness. Then the weighted

irradiance values are summed in the wavelength range from 200-

315 nm to obtain the effective irradiance (Eeff) in watts per

square centimeter (W cm-2). The allowable exposure duration is

obtained from or calculated by dividing 0.003 J cm-2 by Eeff.

Exposure to unprotected skin or eyes should not exceed these

values within an eight (8) hour period. The use of a calibrated

instrument that responds as the relative spectral effectiveness

(Sλ) eliminates the need to perform the weighting

calculations.




The limit values represent situations where nearly all workers

may be exposed without adverse effects. The limits are for

exposures of the eye and skin to UV radiation from arcs,

fluorescent, solar and incandescent sources but not lasers. Laser

radiation must be treated separately and differently due to its

coherent nature.




Such limits may not adequately protect individuals who are

photosensitive or exposed to photosensitizing agents. Tanned

or conditioned individuals may tolerate skin exposure in excess of

the limits. Such conditioning does not, however, guarantee

protection against skin cancer.




Aphakics (individuals with the crystalline lens removed) are a

special problem where UVA radiation may affect the retina (such

radiations are normally absorbed by the lens). Exposure limits do

not apply to these individuals.




The exposure limits should be used as guides in the control of

exposure to UV sources and are intended as upper limits for non-

therapeutic exposure. The limits are not applicable to elective

exposures such as tanning. The limits should be considered as

absolute limits for ocular exposure. The exposure limits were

developed considering a population with the greatest sensitivity

and genetic disposition (lightly pigmented).




The ability to assess a hazard to UV radiation must be expressed

or related to the relative spectral effectiveness as well as

absolute radiometric aspects (descriptive units) of the radiation

under study. The assessor must also recognize the variations of

responses to insults from UV radiation exposure. That is,

thresholds and latent periods from UV radiation exposure vary

with individuals and great variations of the severity of effects are

compounded with difficulties in attaining proper radiometric

measurements.




Basic measurements may be performed using a calibrated broad-

band radiometer with an actinic probe. The probe should be able

to measure in the 200-315 nm range and have a response that

accounts for the wavelength.




Some probes may respond to wavelengths outside the UV range

of interest (such as UVA and visible light), therefore, it is

necessary to quantify or remove this contribution to the reading.

This may be done by making measurements of the UV source

using a blocking filter which absorbs the UV radiation below 315

nm, zeroing the meter, and then making the same measurement

without the filter. This must be done for each measurement of a

UV source under study. Some manufacturers state this is not

necessary with their instrument because selective filtering is

inherent with the probe. Contact the instrument manufacturer

for specific details on this issue. It must be noted that the

spectral range of the instrument is limited by the detector chosen.




Probe placement is important during measurements. The probe

should represent the position of the critical areas (organs) of the

personnel in the occupational setting (i.e. eyes and exposed

skin). Consideration should also be made for possible reflective

surfaces contributing to the exposure of personnel (ceilings,

polished table tops, etc.).




The number of readings depends on the size and number of the

UV sources, habitable areas and the workspace. Measurements

may be taken to assess potential hazards during maintenance

activities (such as close proximity to the source) not normally

performed or conducted by the workspace occupants.




Attempts should be made to determine how long an individual is

required to work in a given area when performing their duties.

Such information is necessary to apply administrative controls

and to compare the measurements.




Allowable exposure durations of multiple work locations must be

considered in the evaluation. These are summed:


T1 + T2 + T3 ... etc.
C1 C2 C3

Where, T = Total time spent at a particular work station

C = Allowable exposure duration at that station




Any value greater than unity would exceed the limits.




Steady state measurements can be made using the

instrument's "normal" mode. Average measurements can be

taken on modulated or flickering light sources if the meter has the

capability to measure with a fast function position. Meters with

an integrate mode can measure flash exposures. Always consult

the manual for the ability of the instrument to measure non-

steady light.




CONTROL

Control measures may be broken down into three areas:

engineering, administrative controls and personal protection.




Effective engineering controls may involve placing the light source

or process within an opaque enclosure or providing a barrier

where the UV output in habitable areas is below the exposure

limits. This must be done without interfering with the operation.

Devices such as key controls and cover interlocks are other

examples of engineering controls. Shields or physical barriers

may control potentially exposed individuals or prevent unsafe

acts from occurring.




Personal Protective Equipment (PPE) is the least desirable control

method, but may be applicable depending on the process. PPE

may consist of eyewear, gloves or other apparel to protect the

skin or eyes. The clothing (hoods, shirts etc.) should be opaque

to the UV wavelengths encountered. UV absorbing eyewear

should be fitted with UV absorbing side shields to minimize the

likelihood of reflections hitting the eye.




Protective eyewear is usually designed to greatly reduce or

prevent particular wavelengths from reaching the eye. This

information must be specified when purchasing such equipment.

Optical density is the variable for determining the attenuation of

the eyewear.




Optical density (OD) is a logarithmic function of the incident

radiation vice the transmitted radiation:


OD = log10 E0
E

Where, Eo is the irradiance of the incident UV

radiation

E is the irradiance of the

transmitted

radiation




Other considerations may be necessary when choosing eye

protection. For example, in the protection from intense visible

light with UV components (such as welding arcs), the eye

protection also needs to be weighted to filter the blue light

hazards.




Topical screening materials have been developed that can

provide partial or sometimes total protection of the skin to UV

radiation. Most screening materials concentrate on filtering the

actinic UV wavelengths. These are known as "sunscreens."

Standard commercial sunscreens permit some UVA to be

transmitted. Although less efficient than UVB, it can contribute to

skin erythema.




Normal work clothing provides adequate attenuation of UV

radiation (OD > 4) produced by common welding operations.

However, some man-made lightweight fabrics, such as nylon, may

transmit significant amounts of UV. Welders should be instructed

in the importance of wearing appropriate dense clothing. Long

sleeve shirts and gloves which can cover exposed skin are clearly

indicated.




UV reflectance from aluminized fabrics may present an additional

hazard. Such material should be avoided in the welding

environment.




Administrative controls consist of establishing standard operating

procedures (SOPs) for the process, education and training of the

user, maintenance and servicing training, warning signs such as

Figure 3 and entry limitations.




Hazard control methods must be chosen to reduce the risk

sufficiently. Even though a method is used to adequately control

the hazard, contingency methods (secondary interlocks) must

always be available for possible circumventions of the establish

methods.

[Harley Scarow]

CAUTION

EYE HAZARD

Do Not Stare Into Light


or


CAUTION

ULTRAVIOLET SOURCE

Eye and Skin Hazard

Authorized Operators Only

SPECIFIC SITUATIONS

General

High Intensity Discharge (HID) lamps (specifically the ones using

mercury) are used in gymnasiums or high ceiling industrial areas.

These may produce considerable UV radiation. Stringent

manufacturing standards exist to assure that an outer jacket is

installed to reduce the risk of UV radiation exposure. Most lamps

are constructed to extinguish if the outer jacket is broken. Lamps

not having this feature will have a warning designating the

potential for exposure. Maintenance personnel must be aware of

the potential for UV exposure on these types of lamps if they

operate with the outer jacket broken. An SOP should be in place

and followed by maintenance personnel during the replacement

of HID lamps.




Selection of paints in the work area can enhance the UV reflection

to personnel. Check with the paint manufacturer for UV

absorptive paints. For most applications, any plastic barrier face

shield or goggle will be effective to protect occupants from UV

exposures from these sources. This is because the

manufacturers of these products add a UV absorbent to deter

aging of the plastics. In situations where any measurable level is

considered unacceptable, the spectral transmission of these

materials should be checked. Interlocks should be installed

where personnel have access to UV sources during maintenance.

Appropriate labeling is necessary to assure that users are

adequately informed.




Clinical

Low pressure mercury lamps are commonly used for germicidal

control in hospitals, and biological laboratory hoods. In most

cases, these lamps are housed in fixtures but may not always

limit direct exposure to eyes or skin of personnel.




Phototherapy and sun lamps are used by physicians to treat

various conditions such as psoriasis. The physician should be

well aware of the dangers of excessive exposure and assure that

such devices are controlled. Ventilation openings may allow

reflections from the source to exit the enclosure.




Because of the potential exposure to individuals of high levels of

UV radiation, therapy and sun lamps must be controlled and

properly used. SOPs are essential and only personnel familiar

with the potential dangers and control measures should operate

the units. They should only be operated in designated areas

which limit direct or reflected viewing to a passerby. Operators

should utilize protective equipment such as shaded glasses and

long sleeved shirts to lessen the risk of UV radiation exposure.




Operating room lamps found in hospitals or dental operatories

are designed to reduce the infrared loading to the patient and

focus the visible light radiation. The glass over the surgical

spotlight filters out UVB and UVC radiations.




The phototherapy units for newborn infants who have

hyperbilirubinemia use special blue lights. In addition to a

potential blue light hazard (not covered in this chapter), the

lamps may produce UV radiation. It is important that plastic or

glass filters be used to protect the infant from UVB radiation. The

nursing staff should not be at risk from these devices, however,

the lamp should not be stared at directly. Operators should

ensure the plastic or glass filter remains in place and that labels

are in place to alert personnel to potential hazardous emissions.




"Black Lights""Black lights" are often used along with

fluorescent powder for non-destructive test procedures. These

lamps normally produce wavelengths in the UVA range. These

lamps are normally not a problem unless the lamp envelope itself

does not sufficiently filter out the actinic UV lines of the mercury

spectrum (297, 303, 313 nm). Also, any individual who is

photosensitive (such as the result of taking medication) may elicit

a severe response when using such equipment.




Some "black light" units have a mode to specifically produce UVC

or UVB radiation. Such units should be evaluated or reference

data from the manufacturer consulted to address potential

hazards to personnel.




Control methods include positioning the lights so that individuals

are not chronically exposed. The lamps should also be used in

designated areas, free from reflective surfaces. Protective

eyewear and long sleeve shirts or gloves may be necessary.




Curing Operations

In graphic art facilities, arc lamps or tungsten halogen lamps are

used to make negatives and photo offset press plates. The glass

platens will usually eliminate UVB or UVC radiations from the

lamp. However, the units should be located away from traffic

areas and employees cautioned to avoid staring at the exposed

lamps. Most flip top platemakers reduce glare and eliminate

safety concerns but the operator should not stand over the slit

that exists on the top of these units. It may be advisable to

utilize UV filtration glasses if the operator must stand over the

unit when it is in use.




Duplicating machines that are often found in offices and print

shops contain light sources that may produce UV radiation. The

glass platen will almost always remove the UVB and UVC

radiation. Operators are still cautioned not to stare into the light

source when document covers are opened/removed.

Manufacturers' light source emission data should be consulted on

graphic arts and duplicating machines to assess hazard risks to

maintenance personnel when the normal safety barriers are

violated.




Some selected sources of UV are provided as examples in Table

3. The irradiance values are provided as a relative indication of

the hazard potential of the source. These values may vary

considerably. The values also do not account for potential blue

light hazards.

[Harley Scarow]