不同波段紫外線對人體影響

紫外線探傷燈，俗稱紫外線燈，是無損探傷、脫脂清洗檢查、熒光泄露撿漏……中用于激發熒光染料/物質的光源。隨著人們安全意識的提高，在購買和使用紫外線燈的時候總會問：使用紫外線燈對身體會有什么傷害？使用的過程中我應該怎么去保護自己？帶著這些問題，我們來看看。

在紫外線燈還是處于高壓汞燈的時候，在國外就用和紫外線燈同類種的紫外線燈作為美黑設備，在專業人士的指導下，照射皮膚，使皮膚變成古銅色。紫外線的波長分為長波（UVA）、中波（UVB）、短波(UVC),不同波段的紫外線對人體的傷害是不太一樣的：

UVA波段：波長320～400nm，又稱為長波黑斑效應紫外線。太陽光中含有的UVA有超過98%能穿透臭氧層和云層到達地球表面，UVA可以直達肌膚的層，破壞彈性纖維和膠原蛋白纖維，將我們的皮膚曬黑和老化。長期暴曬，可以導致皮膚產生癌變。

UVB波段：波長275～320nm，又稱為中波紅斑效應紫外線。太陽光中含有的UVB大部分被臭氧層所吸收，只有不足2%能到達地球表面，在夏天和午后會特別強烈。UVB紫外線對人體具有紅斑作用，能促進體內礦物質代謝和維生素D的形成，但長期或過量照射會令皮膚曬黑，并引起紅腫脫皮。此類紫外線的極大部分被皮膚表皮所吸收，不能再滲入皮膚內部。但由于其階能較高，對皮膚可產生強烈的光損傷，被照射部位血管擴張，皮膚可出現紅腫、水泡等癥狀。長久照射皮膚會出現紅斑、炎癥、皮膚老化，嚴重者可引起皮膚癌。

UVA和UVB對皮膚的輻射深度示意圖

UVC波段：生物學稱為短波滅菌紫外線，波長200～275nm，又稱為短波滅菌紫外線，太陽光中含有的UVC完全被臭氧層所吸收。UVC對人體的傷害很大，短時間照射即可灼傷皮膚，長期或高強度照射還會造成皮膚癌。紫外線燈發出的就是UVC短波紫外線（臭氧層的減少和皮膚癌的增多有直接關系）。

紫外線燈（黑光燈）需要的紫外線光為365nm附近的光譜，這段光譜對熒光物質的激勵效率高。對于LED冷光源紫外線燈，光輻射95%以上都是在365nm附近的UVA成分，不含有UVB和UVC成分，即紫外線燈對人體造成的影響就是UVA波段對人體的傷害“直達肌膚的層，破壞彈性纖維和膠原蛋白纖維，將我們的皮膚曬黑”，短時間的照射對皮膚基本無傷害，那這個短時間怎么去界定？

根據美國政府工業衛生學家會議（ACGIH）的規定：工業探傷紫外線燈歸類為3級UV危險源，針對長波段紫外UVA，每年人體可以承受的紫外zui大輻射劑量為3333kJ/m2，每八小時zui大照射量為10kJ/m2。而一般的工業紫外線燈照度在5000uW/cm2(=50W/m2)左右；按此計算，人體裸露皮膚被紫外線直接照射的時間不應超過200秒。因此，做熒光檢測時，必須佩帶紫外線防護手套，避免人體的皮膚被直接照射到。另外紫外線直射眼睛傷害很大，作業時應佩戴紫外線防護眼鏡。

What is the Difference between UVA UVB UVC?

 Which is Most Dangerous?

UVA, UVB, UVC- all of these are forms of ultraviolet light rays that are naturally occurring, but they are not created equal. We'll explain the differences between these three forms of radiation, and then discuss how UVC is harnessed in man-made lighting products to inactivate pathogens (kill germs).The sun is responsible for emitting each of the different types of ultraviolet light. UV rays are also found in man-made products, like tanning beds and welding torches. Although UV rays have some benefit, namely encouraging vitamin D production in humans, everyone should practice caution as each form of UV comes with its own risks.

UVC
UVC is the shortest wavelength of the three forms of UV. The shorter the wavelength, the more harmful the UV radiation. However, lucky for us, UVC isn't able to penetrate earth's atmosphere. So while UVC is the most dangerous because it's the shortest wavelength, it's not a risk to the typical person because the sun's natural UVC emissions don't penetrate skin. Remember, they actually do not even penetrate earth's atmosphere naturally at all. UVC is absorbed completely by the ozone layer.

This is not to say that UVC isn't dangerous. Although naturally occurring UVC doesn't permeate earth's atmosphere, inorganic sources of UVC radiation exist and are dangerous when not used properly. So, the people who need to be concerned about UVC radiation are those working with these man-made sources of UVC, like welding torches, mercury lamps, and, you guessed it, germicidal UV-C lighting, which we distribute. More on this after we define UVA and UVB.

UVB
UVB is the second shortest wavelength and the main culprit of sunburn. It's mostly absorbed by the ozone layer but still gets through (about 5% gets through overall). It harms the top layer (epidermis) of your skin in as little as 15 minutes of sun exposure. UVB rays are stronger or weaker depending on the time of day and season. There is a strong link between UVB rays and skin cancer. UVB rays do age skin over time.

UVA：
UVA is the longest wavelength, penetrating the deepest and causing the vast majority (upwards of 95%) of UV radiation getting through earth's atmosphere. This is the form of radiation that causes skin aging, like spots and wrinkles, because it does reach so deeply into skin layers (through to the dermis layer). UVA rays can tan your skin right away, and do appear to be linked to cancer. UVA rays, unlike the others, penetrate glass and clouds, causing harm on overcast days or via your windshield.

Protect Yourself
You should protect yourself from UVA and UVB rays by applying broad spectrum sunscreen, wearing UPF clothing and sunglasses, and blocking UV rays with umbrellas and car shades as needed.

Most Dangerous?
So, which is the most dangerous type of UV radiation? There isn't a good answer to this question, although it's asked frequently. On the one hand, UVC is the most dangerous because it's the highest energy portion on the UV spectrum. However, UVC is completely absorbed by earth's atmosphere so it's really not a risk to most people. It's only a risk to those exposed to artificial sources of UVC (see more below).

If we choose the most dangerous based on exposure, then UVA is the clear forerunner for danger. It accounts for nearly all UV exposure as it's barely blocked by the earth's atmosphere. That said, it's also the shortest wavelength and isn't thought to cause as much long-term damage as UVB from the sun.

Although only a small amount of UVB penetrates earth, we'd consider it the most damaging to your average person (not those working incorrectly with artificial UVC sources) because it comes with the highest skin cancer risk.

Artificial UVC
All forms of UVC radiation are artificial since the sun's UVC doesn't get through earth's atmosphere, as discussed. Some common sources of man-made UVC radiation are:

Older tanning beds
Lasers
Mercury lamps
Welding torches
Germicidal UV-C lighting
Not all artificial forms of UVC are equal in risk/reward. For instance, tanning beds are unnecessary and dangerous and should be avoided. Don't purposefully expose yourself to harmful radiation (note that most modern tanning beds use UVA radiation, which is still dangerous). Welding torches, conversely, are necessary for some jobs, and using the proper protective gear mitigates the risk of your UV exposure. Also, becoming a welder takes lots of training; they're prepared for this risk.

Germicidal UV-C lighting, when used properly, is operated in empty spaces using controls for safety. The reward of having killed up to 99.99% of pathogens from, say, personal protective equipment (PPE), outweighs the nearly non-existent risk of UV exposure.

Moreover, not all artificial UVC sources operate at the same wavelength. While UVC in general encompasses wavelengths of 100-280 nm, it varies from product to product where they are in that range. For example, one lamp that we distribute operates at 254 nm.

In conclusion, if you were to be exposed to artificial forms of UVC radiation, it would be detrimental (we talk about this in more detail here) but as long as equipment is used as directed, the benefits of UV-C technology outweigh the risks in most cases. It's like any technology- will the radiation from an x-ray machine harm you? Yes, but we have controls in place to ensure that the radiation from an x-ray machine can't harm you, and we won't stop using x-ray machines just because of this risk.