Can radiation from subway security checks really lead to a shorter life?

At present, many cities such as Beijing, Wuhan and Shanghai have implemented regular security checks on subways. Some people worry that the radiation from X-ray security scanners is harmful to the human body, saying that "being exposed to radiation once a day will shorten a person's life by one day." For this reason, some passengers even refuse security checks. So, does the radiation from security equipment really affect health?

Question 1: Is the radiation from security scanners harmful to health?

Baggage X-ray security scanners, like medical X-ray diagnostic scanners, obtain images of the interior of the object by irradiating the object with X-rays. However, the radiation dose of parcel security scanners is much smaller than that of medical X-ray diagnostics because the images obtained from parcel security inspections do not need to reach the resolution of medical diagnosis levels. According to the national standard GB 15208.1-2005, the single inspection dose of the X-ray security scanner should not be greater than 5μGy. At the same time, the X-ray dose at any point 5cm away from the outer surface of the equipment (including the equipment entrance and exit) should be less than 5μGy/h. This standard is the same as the US FDA standard. In fact, the radiation dose of X-ray security scanners used in subways and airports is much lower than that stipulated by national standards.

When the lead curtain at the entrance and exit of the security scanner was pulled open, the highest data was displayed on the portable radiation detector held by the technician at the entrance and exit. After calculation, the technicians said that using the highest data as the calculation standard, if a passenger takes the subway every day for 365 days a year, and pulls up the lead curtain every time when passing through security check, and each time the lead curtain is pulled up for 5 seconds, then the effective dose of radiation received by this passenger each year is less than 0.007mSv (millisievert).

According to the national "Basic Standards for Ionizing Radiation Protection and Radiation Source Safety", the annual radiation dose received by a normal person should not exceed 1mSv. my country's standards are formulated based on the standards of six authoritative international organizations, including the United Nations Scientific Committee on the Effects of Atomic Radiation and the International Atomic Energy Agency. Even when used as a reference worldwide, they are relatively stringent.

The rays inside the security scanner are basically direct and are all sealed inside the security scanner. There is still a very small amount of scattered rays, but the lead curtains at the entrance and exit of the security scanner can basically block it. In addition, the four walls inside the security scanner are all thick lead walls. As long as the lead curtains are not lifted up significantly, the security scanner cannot detect rays around it.

Although the radiation dose of the security scanner is very small, it is still recommended to stay away from the exit as much as possible, or shorten the time spent at the exit. You should wait until the goods pass through the curtain and the curtain is completely lowered before picking up your luggage.

Question 2: If I take the subway every day, will the accumulated radiation be harmful to my body?

We currently have no clear data on how much radiation dose the average passenger receives each year due to security checks. But compared to ordinary passengers, security scanner operators will obviously be exposed to more radiation, especially airport baggage security personnel, who often need to manually load or unload luggage from security scanners. In 2003, the U.S. Centers for Disease Control and Prevention conducted a large-scale radiation dose survey on baggage security personnel at the six major airports in the United States. The results of the survey report showed that the vast majority (89%) of airport baggage security personnel received an average annual radiation dose of less than 12mrem, or 120μGy, due to their work, and the remaining few personnel basically received less than 60mrem, or 600μGy. According to data from the United Nations Scientific Committee on the Effects of Radiation report, the average annual upper limit of radiation exposure for the general public, excluding natural radiation and medical radiation, is 1000 μGy. Even for airport baggage security personnel, the radiation dose they receive due to their work is mostly far less than this upper limit. The American Society of Health Physics also pointed out that the radiation dose of luggage X-ray security scanners is much smaller than that of medical X-ray machines and is already fully shielded.

Question 3: Does the security scanner have any impact on the items being scanned?

Since the radiation from baggage X-ray security scanners is very small, the impact on the scanned items themselves is negligible. But there is one special item - film - that is more sensitive to X-ray radiation. According to the results of an experiment conducted by the National Association of Photographic Manufacturers (NAPM) in 1994 on films of different sensitivities from different manufacturers, ISO1600 films showed no imaging abnormalities after 16 X-ray baggage scans, but slight imaging abnormalities were found after 100 scans. Kodak has given the advice that "film with ISO 400 or above should not be subjected to X-ray security inspection." According to data from Gao Jing, the supplier of security equipment used by the Shanghai Metro, one of its models with the highest single dose (its single dose is close to the limit value specified by the national standard) also has the ISO1600 film safety mark. The photographic films we use daily have a sensitivity of mostly below ISO400. On the whole, it is generally believed that ordinary photographic film (excluding X-ray film or other films with stringent imaging requirements) is safe to pass through the security equipment currently used in airports and subways under normal travel conditions. However, since the impact of X-rays on film is cumulative, high-sensitivity films should be prevented from passing through X-ray security checks multiple times. It should be pointed out that X-rays have no effect on digital cameras, so they can pass through security checks without worry.

In addition, unlike the radioactive element particles leaked in the Fukushima nuclear accident, X-ray scanning does not cause radioactive contamination. After the scan, no radioactive substances will remain on the luggage, and food scanned by X-rays will not be harmful to human health.