Wittlich's formula

Formula for calculating the occupational (insured) UV exposure (Hb) in a defined time unit. The formula is widely used by accident insurance providers.

Note: The following explanations correspond to a shortened and varied version of the "Technical Information BK-Cases BK No. 5103" of the IFA from February 2015 (see Lit.)

Wittlich's formula is structured in such a way that additions or deductions are made to a reference value - Hb/a (ref) - by individual factors. These factors can be subdivided:

• Time factors
• geographical factors
• personal factors

There are two ways of calculating the working conditions: activity ratios in days of the week or months or in shifts per year.

• Hb/a =∑fWT x fMS x fb x fTZ x fLAT x fHeight x fReflex x fBody x fProtection x Hb/a(ref)
• ∑fWT x fMS x fJZ x x fb fTZ = Time factors by days hours
• ∑ fLAT x fHeight = geographical factors
• ∑ fBody x fProtection = personal factors

Hb

Hb - defined as " annual occupational (insured) irradiation " - is made up of the sum (∑) of all irradiations acquired in the course of insured activities during one year. Each activity during this period must be specifically identified, presented and calculated,. The total exposure is determined by adding the individual periods.

a = age of the insured person in years on the day on which the diagnosis was confirmed.

Time factors:

∑fWT x fMS x fJZ x x fb x fTZ = Time factors by days/hours: The time factors (f) make it possible to take into account both the days worked in a given activity and the other hours spent outdoors. Two factors are available for days (fMS or fJS) and for hours (fb or fTZ). In addition, a factor can be used to take into account how many days per week an activity has been performed (fMT).

fWT:

The factor "f" for working days per week (fWT) currently corresponds to 1.0 for a 5-day week. If the insured person performs overtime, an upward adjustment is made. If the insured person works less, the adjustment is made downwards. For daily bonuses or deductions, 1/5 is added or deducted accordingly.

For one working day worked, this results in an fWT of 0.2, for 2 working days an fWT of 0.4, for 5 working days an fWT of 1.0, and so on.

fMS:

The factor "f" for M= assembly/ S= seasonal work refers to an activity that is not carried out throughout the year. The factor fMS is used to indicate the corresponding proportion. For a month worked, the fMS is 0.08 - for 2 months worked, the fMS is 0.17 - for 12 months worked, the fMS is 1.0. The factors fMS and fJZ (seasonal factor) are directly related. If one of the two factors is used, the other factor must be set to 1.0. Thus it is not mathematically valid.

fJZ:

the factor - fJZ -"Seasonal factor" defines the period of activity within a year. It thus takes into account the different positions of the sun in the different seasons, and thus different irradiation. Although this factor "latitude" is dependent, the factors calculated for the individual months are calculated for the 50th latitude (for example Germany). By definition, these values are currently also valid for all places in the world. To take into account employment lasting several months, the individual values of the months are added together. For activities in the southern hemisphere, the seasons shifted by half a year must be taken into account.

Hours

Activities that are not carried out out outdoors all day are evaluated by the hourly factors fb and fTZ (time of day factor). Both factors are mutually dependent.

fb

The factor - fb - is used to specify proportions of working time outdoors if these cannot be related specifically to certain hours of the day. If the activity is carried out out outdoors during the entire working time, the factor is 1.0. 4 working hours for an 8-hour working day would be valued with the factor - fb = 0.5.

fTZ

the time of day factor - fTZ - takes into account the exact period of outdoor work on one day. It takes into account the fact that the intensity of UV radiation changes over the day with the different positions of the sun. It distinguishes between summer and winter time and shows different values from hour to hour. If the activity is carried out over several hours, the factor to be used for TC is the addition of the individual values. For exposure times of 8 hours per day, a - TC - of 1.0 is applied. In the case of year-round employment, only the daytime factors of summer time are used (Reason: the relevant irradiation takes place in summer time)

Geographical factors

The geographical factors

• fLAT (latitude factor)
• fHeight (height factor)

evaluate the changed solar zenith (this changes the irradiation more strongly) at other latitudes (fLAT), at higher altitudes (fHeight) and with the reflection factor (fReflex) the reflections of UV rays through different surfaces such as water, snow, sand or grass.

For the latitude factor, the reference value for Germany is set at 1.0. Furthermore it was determined that activities in more northern areas (higher than 55th latitude) are also assessed with 1.0.

Activities in different heights above sea level are taken into account by the height factor f-height. For Germany an altitude factor of 1.0 applies with the exception of the higher mountainous regions.

fReflex

The reflection factor - fReflex - takes into account the additional radiation caused by reflecting surfaces. It is defined as the sum of direct radiation (factor 1.0 applies here) and additional (indirect) radiation from reflecting surfaces. In the reference irradiation - see Hb/a(ref) - there are already unspecific parts of reflecting surfaces. The additional reflection should only be taken into account if the reflections are 30% or > 30% ( fReflex=0.3 or 1.3) and the activity has taken place predominantly on this surface.

Personal factors

The personal factors fbody x fprotection refer to a body site factor "fbody" which takes into account the different exposures of individual body areas. The factor "fProtection" is applied if protective measures can be proven by evidence.

fBody (body part factor)

The body site factor "fbody" evaluates the UV exposure of the different areas of the body. The effect of UV radiation on the body surface depends on its angle of incidence. fBody describes the ratio of the average exposure of an affected body area in relation to the breast position (reference site). If the different exposure factors are ignored, the body position factor is set to 1.0 in the calculations until further notice.

fProtection (influencing factor for protective measures)

The influence factor for protective measures "fProtection" is to be applied if a protective measure can be clearly proven. This factor includes personal protection factors but also other protection mechanisms (e.g. glass panes). The following applies to the definition of the protection factor: a factor of 0 is specified if a protective measure has been clearly proven at the location of the disease. If no protective measure has been assigned, the factor is to be assessed as 1.0. If the UPF (UV protection factor) is used (factor is partly shown in the clothing), the protection factor "fProtection" is calculated as the reciprocal of the UPF (1/UPF).

Hb/a =∑nn x Hb/a(ref)

• Hb/a(ref) Reference value
• Hb = long-term occupational radiation of a person employed in Germany
• a: Age of the insured person in years on the day the diagnosis was confirmed

The annual reference value for the full-time outdoor workers in Germany is 300 SED (SED = standard erythema dose, 1 SED = 100 J/sqm erythema-weighted irradiation). This value takes into account the usual weather conditions in Germany. It applies to the breast position.

Evaluation of UV exposure as an occupational disease

According to §9(1) SGB VII, occupational diseases are diseases caused by special influences to which certain groups of people are exposed to a considerably higher degree than the rest of the population due to their insured activity. In case law, it is often assumed that this criterion is fulfilled in the case of a doubling of risk. It is accepted that due to a "superadditive" dose-effect relationship, an additional occupational exposure of 40% results in an additional risk of 100% (doubling).

The technical working conditions are considered to be fulfilled if at least an insured lifetime portion Hb,min of 40 % is added to the private exposure Hp. Hb/min = 0.4 x a x fbody x 130 SED

1. Braakhuis BJ et al (2003) A genetic explanation of Slaughter's concept of field cancerization: evidence and clinical implications. Cancer Res 63: 1727-1730
2. Diepgen TL et al. (2015) Reduction of earning capacity in BK 5103 " Squamous cell carcinomas or multiple actinic keratoses of the skin due to natural UV radiation " Dermatology at work and in the environment 63: 3-7
3. DGUV work aid "Skin cancer due to UV radiation". www.dguv.de/ifa
4. Slaughter DP et al (1953) Field cancerization in orally stratified squamous epithelium; clinical implications of multicentric origin. Cancer 6: 963-968
5. Wittlich M (2015) IFA (Institute for Occupational Safety and Health of the German Social Accident Insurance. Technical information for the determination in occupational diseases(BK.) - cases against the background of the new occupational disease with the BK no. 5103 "Squamous cell carcinomas or multiple actinic keratoses of the skin by natural UV radiation". www.dguv.de/ifa