Comment by hammock | Hacker News Reader

Comment by hammock | Hacker News Reader

I wonder about the increasing use of x-rays in non-medical applications. Industrial applications, or even with the public- like the backscatter machines that TSA and police forces use. Therac-25 seems to be the only story we have where something went wrong - but what are the chances a bad thing could happen, or already happened, in another machine?

TSA employees are not permitted to wear dosimeters[1], which makes it hard to detect these things. Scientific American, the most established magazine in the US, is among respected bodies that have recommended dosimeters for accountability reasons.[2]

There are also extremely infrequent (and sometimes rigged) studies done on the equipment, and they often find dangerous conditions. For example:

>Doses for some of the baggage screeners exceeded the maximum dose for the public.... Some EDS machines were not well maintained (i.e., they had bent curtain rods and missing curtain flaps).... Most EDS machines emitted low levels of radiation; a few exceeded regulatory limits.[2]

[1]https://www.tsa.gov/blog/2011/06/30/tsa-cancer-cluster-myth-... [2]https://www.scientificamerican.com/article/airport-screeners... [3]https://www.cdc.gov/niosh/hhe/reports/pdfs/2003-0206-3067.pd...

TSA Officers aren't permitted to wear dosimeters on the job.

PRetty damning, if you ask me.

Here's their fationale from teh FAQ in the linked article [1]

"Q: Why aren’t your officers permitted to wear dosimeters?

A: There is a really good reason for this. The emissions from our X-ray technology are well below the requirements that would require their routine usage. To help reassure passengers and employees that the technology is safe, however,health physicists with the U.S. Army have been conducting area dosimeter surveys at multiple airports nationwide."

This is at best massively flawed reasoning by the TSA, and at worst a deliberate misleading rationale.

1) While the NORMAL dosage is of course well below any level that would make a dosimeter useful, a dose from a malfunction or bent/broken/missing shield panel could easily exceed dosimeter detection thresholds.

2) Spot checks are nice, but unless they are very frequent, they could easily miss a malfunction and leave it overdosing agents and people for a long time. Even if inspections are every 6 months at every airport station, that will leave a malfunction overdosing people for on average, three months.

3) Detecting, identifying, and repairing a malfunctioning system could be done much sooner and at lower cost by using dosimeters, either on employee volunteers or just hanging them on the chairs & workstation surrounds.

It is this kind of frankly stupid stick-your-head-in-the-sand reasoning that breeds distrust of governments and the companies that supply them.

[1] https://www.tsa.gov/blog/2011/06/30/tsa-cancer-cluster-myth-...

I'll give them the benefit of the doubt and say this is poorly worded. TSA officers also aren't permitted to hygrometers on the job. Why? Because there's no point to wearing a hygrometer as a TSA officer. Unlike with the dosimeter, that doesn't need to be spelled out.

That doesn't mean they aren't allowed to perform dosimeter readings at all, it just means it's not acceptable to carry this equipment around all the time.

> While the NORMAL dosage is of course well below any level that would make a dosimeter useful, a dose from a malfunction or bent/broken/missing shield panel could easily exceed dosimeter detection thresholds.

Do you actually know that these could be harmful, or is it just a suspicion?

TSA officers may not be offered hygrometers, but I doubt if there is anything explicitly preventing them from carrying their own hygrometer - actively preventing officers from carrying dosimeters seems more likely to be tied to prevent any long term lawsuits. We get bombarded by all sorts of radiation throughout the day, describing a malignant skin mole to a back-scatter vs. the sun isn't something you could do without evidence. The collection of such evidence is specifically being prevented.

So I'd assume this is more like coal miner operators in the 1800s planning ahead to protect themselves from the eventual outbreak of black lung.

I won't give them the benefit of the doubt on poor wording (they have plenty of time and resources to get it right).

As far as we know, there is no general ban on wearing instrumentation of any other on the job, unless it is somehow clumsy and would interfere with their duties or the appearance of their uniform.

In contrast, the simplest dosimeter is typically a very small patch of photographic paper in an envelope opaque to visual light but transparent to harder radiation (towards the gamma end of the spectrum). It is like an inch square, or like a typical nametag, easily worn in a shirt pocket, no more visible to anyone else than a credit card in the shirt pocket.

The only plausible reason to forbid this is to prevent any kind of whistleblower event.

Of course I do not know the actual levels of radiation inside each machine or all of their possible failure modes. However, we do know

1) high-energy radiation dosage is cumlulative -- each day's dose adds up, so if you have 1/100th of a critical dose each day in a workzone, in less than four months, you should be banned from that work zone. This is the way it works in many facilities dealing with radiation sources, and everyone wears dosimeters which are checked, and people are reassigned when the total dosage exceeds the prescribed level.

2) There are medical limits on how many x-ray and CT-Scan procedures are allowed for patients, again due to the cumulative nature of radiation exposure. Even with the very low-doses of modern machines, these are a concern and are tracked (I know this from the experiences of several close family members).

3) The TSA machines do produce sufficient radiation in their beam to fog ASA800 and higher film. This is definitely a non-trivial dose. Tho obviously not lethal in a single dose (e.g., if you rode through the machine), it is significant. If an interior shielding panel is bent or somehow mis-installed during manufacturing, maintenance, or repair, it is entirely plausible that people working regularly in the area of the leaking radiation could be overexposed.

So, no, this is not even close to mere suspicion or Luddite "ooh radiation bad" -- and yes, we do know that these could be harmful, especially over extended periods.

I hope you are not an employer with that attitude.

> As far as we know, there is no general ban on wearing instrumentation of any other on the job, unless it is somehow clumsy and would interfere with their duties or the appearance of their uniform.

Who is "we"? Aren't you just pleading ignorance here? What do really you know about what TSA agents can and can't wear? Anything can "interfere" with the appearance of a uniform, including a "small photographic patch".

> The only plausible reason to forbid this is to prevent any kind of whistleblower event.

Then why do they do allow third party monitoring?

Having further looked into this, the page you posted is outdated and they ended up handing out dosimeters themselves:

https://www.livescience.com/36079-airport-security-screening...

The result was negative. Of course you can't prove a negative, maybe there's radiation somewhere else where they didn't look...

> 2) There are medical limits on how many x-ray and CT-Scan procedures are allowed for patients, again due to the cumulative nature of radiation exposure.

> 3) The TSA machines do produce sufficient radiation in their beam to fog ASA800 and higher film. This is definitely a non-trivial dose.

According to: https://www.radiologybusiness.com/topics/business-intelligen...

" TSA claims the “backscatter machines” cannot produce more than 0.005 millirem of radiation per scan. In comparison, the agency says, a chest x-ray exposes patients to 10 millirem of radiation, and the maximum recommended exposure to radiation from man-made sources is 100 millirem per year."

That would mean that if you had a machine that was completely unshielded, you would have to perform 2000 scans to get the equivalent of a chest X-Ray. Compare that to the radiation exposure of your average flight attendant.

>> Anything can "interfere" with the appearance of a uniform, including a "small photographic patch".

Not if it is inside your pocket. Get real.

>> Then why do they do allow third party monitoring?

Obviously because they can control when it is done as well as how the results are distributed, or not distributed.

>> " TSA claims the “backscatter machines” cannot produce more than 0.005 millirem of radiation per scan. In comparison, the agency says, a chest x-ray exposes patients to 10 millirem of radiation, and the maximum recommended exposure to radiation from man-made sources is 100 millirem per year."

>> That would mean that if you had a machine that was completely unshielded, you would have to perform 2000 scans to get the equivalent of a chest X-Ray

1) this assumes that the "0.005 millirem per scan" is the total output of the machine, including all radiation absorbed by the lensing & shielding. We do not know if this figure is the total generation output, or only the total amount put to the target & receiving sensors.

2) one thing we do know is that the radiation will NOT be scattered evenly; there will be lobes and hotspots and cold spots.

3) even if we assume .005millirem/scan, at the rate of two/minute, that's 1000 minutes to get a chest x-ray, or 16 hours, basically two work days. In LESS THAN ONE MONTH, they are over the yearly dose.

More importantly, this is only counting the backscatter machines that are specifically designed for super-low doses as they are specifically irradating people.

This does NOT look at the luggage scanners, either for carry-ons or for checked luggage, which likely have much higher outputs.

Finally, even if your arguments are correct and there is truly no risk, there should be no problem at all for officers to wear their own dosimeters -- the results would merely be putting their minds at ease that they are not getting exposed.

Thus, we are back to the only reason to prevent officers from wearing dosimeters is an attempt to control the information and prevent whistleblowers and/or lawsuits.

Again, I sincerely hope you are not an employer with this attitude.

> Obviously because they can control when it is done as well as how the results are distributed, or not distributed.

Let's apply some Occam's Razor here.

I am led to believe they know that these machines are harmful and therefore they are carefully orchestrating all testing of these devices by, among others, all of the following parties: "U.S. Army Public Health Command, the Food and Drug Administration’s (FDA) Center for Devices and Radiological Health (CDRH), the National Institute of Standards and Technology (NIST), and the Johns Hopkins University Applied Physics Laboratory (APL)".

That's all done to prevent some sort of mass lawsuit, which might cost the United States some money.

The simpler explanation is that TSA rules are simply really strict, because that's just how TSA rules are.

https://www.quora.com/Are-TSA-screeners-permitted-to-wear-ra...

The rules don't have to make sense. There's a whole lot about the TSA and its procedures that doesn't make sense.

> We do not know if this figure is the total generation output, or only the total amount put to the target & receiving sensors.

I'm content with the description given that these machines "cannot produce" more than that. You can do your own research on the matter.

> 3) even if we assume .005millirem/scan, at the rate of two/minute, that's 1000 minutes to get a chest x-ray, or 16 hours, basically two work days. In LESS THAN ONE MONTH, they are over the yearly dose.

...assuming no shielding whatsoever. You would hope that after two months without shielding on the device, someone might notice. Even then, such exposure would be well below the occupational limit for radiation workers (5000 millirem):

https://ehs.stanford.edu/manual/radiation-protection-guidanc...

> This does NOT look at the luggage scanners, either for carry-ons or for checked luggage, which likely have much higher outputs.

Fair enough, but you picked an article that was specifically concerned with those backscatter devices.

>>I am led to believe they know that these machines are harmful and therefore they are carefully orchestrating...

That's not even close to the simplest explanation. Far simpler is that they are careless, clueless, and paranoid, and don't want anyone finding out something bad on their watch. Or they just don't want to allow anyone to get concerned.

>> The rules don't have to make sense. Unless we're living in a Kafka or Vonnegut book, they are supposed to have actual reasons and make sense.

Calling out one particular type of measuring device, which happens to measure the one plausible type of hazard in that workplace, yeah, that's suspicious.

>> .assuming no shielding whatsoever. Does not assume no shielding whatsoever, only a plausible hotspot or focus. The point is that the potential dosing is in the range of values that could cause a hazard, and even at 10% of that value, would be overdosing within a year. It is not like it is totally off the scale (as are many of the public's fears).

>> You would hope that after two months without shielding on the device, someone might notice.

Yes, you would hope that. However, if you've ever read reports on industrial issues, you'll find that far worse and more noticeable hazards go unnoticed/unfixed for YEARS at a time before they get around to killing someone. And this sort of low-level radiation is particularly pernicious, as it is completely unnoticeable until after it is too late.

The simple solution is, assuming that these machines are largely safe (which I generally expect), is to say "you can buy dosimeters on your own dime and wear them if you like, just keep them out of sight in your pocket while on duty. If anyone gets any unexpectedly high readings, we'll investigate, but remember since you haven't got a chain of custody around the meter, it'll be only the beginning of an investigation, not immediate acceptance of your results."

Ye, it may turn out to be bit more work, but it shows you're on the side of worker safety, and on the road to getting things fixed. Mostly, it'll quell any fear and likely cause no one to wear one.

With the rules as it is, I'd be damn sure to sneak dosimeters into my clothes while working there.

Therac-25 is definitely not the only incident involving radiation in medical applications:

https://www.cbc.ca/news/canada/hamilton/radiation-treatment-...

http://indico.ictp.it/event/a12208/session/65/contribution/4...

Those are great resources. Thanks.

>> but what are the chances this could happen, or already happened, in another place?

Zero. The TSA machines are not limited by software. They will catch fire themselves before killing people. Therac-25 was designed to destroy tissues, cancer tissues but human tissue nevertheless. It is like comparing an m-16 to a rubber band gun. They are both guns, but they are fundamentally different in terms of capabilities with the former.

The parent is talking about scanners including those luggage x-ray machines, which can slowly dose up and give cancer to their operators.

Over a very extended period. They wont cook people like the therac did.

Extended periods are very relevant to any TSA employee that can hold down the job. Death is death, flashy or not.

All xray backscatter imaging devices were removed by the TSA and replaced with millimeter backscatter. The downside is those xray backscatter devices went to prisons for use.

>All xray backscatter imaging devices were removed by the TSA

At the airports. They still exist in prisons, in covert trucks and other mobile units owned by TSA and law enforcement, and potentially in other venues of public transportation, stadiums and arenas, etc.

X-rays are also in INCREASING use at airports, since they are in the process now of replacing the carry-on bag scanners with CT scanners. A CT scan gives a 3D image of your luggage which means you don't have to take out your laptop. Unfortunately, a CT scan also uses 10X more radiation than a regular x-ray.

The problem is two-fold:

1. Xray scanning should be outlawed for public safety use in humans. You want to scan humans? You must use millimeter wave, and the cost is on you.

2. Governance. It's perfectly acceptable to use CT scanners for non-human surveillance (carry on bags, checked luggage, etc), but you must ensure life safety is enforced. If you don't, steep penalties up to and including jail time.

Call your reps, run for office, vote for people who care about this.

Up here in Canada I'm happy to walk through a metal detector as part of the security screening... and then board on my plane to a destination I hope doesn't include the US to avoid the hassle of American security theater.

When I was still in VT I was happy to see that our third tier airport managed to hang on the noticeably more effective metal detectors long after other areas phased them out, sadly they've now been swapped out.

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