仔細看：新的雷射光實驗揭示了大便顆粒在我們沖水後可能爆噴的程度

前所未見的浴室物理學研究。

資料來源：MAX G. LEVY / 自然 / 財團法人台灣紅絲帶基金會編譯

 

圖片來源：約翰·克里馬爾迪

 

今年夏天，在科羅拉多州的博爾德，約翰·克里馬爾迪 (John Crimaldi) 和他的土木與環境工程師團隊聚集在廁所周圍——為了科學。

他們在無蓋馬桶上方放置了一個雷射光以發出綠光：如果在衝馬桶時出現任何通常不可見的顆粒，他們假設，它們會散射光並顯示為綠點。 為了記錄便盆動態，該團隊在幾英尺外安裝了攝影機。 然後……沖洗。

接下來發生的事情讓研究人員沉默了。「我們都驚呆了」，克里馬爾迪回憶道。「我們看到這股能量驚人的粒子射流沖向天花板」。

他們的雷射光捕捉到一團飛向空中的粒子雲或羽流——然後在那裡徘徊。「人們剛剛開始大笑。他們就像，『哦，我的上帝，你一定是在開玩笑吧。這就是你衝馬桶時發生的事情？』」

科學家們將雷射光聚焦在馬桶上，以揭示便盆顆粒可以移動多遠。

科羅拉多大學波德分校 (CU Boulder) 最新消息——在今天發表在《科學報告》上的一項研究中，來自科羅拉多大學的 Crimaldi 團隊他們的雷射光裝置可視化無蓋馬桶如何比以往任何時候都更詳細地描述了羽流。

十多年來，研究空氣中看不見的顆粒的科學家報告說，無蓋公共廁所可以將含有尿液、糞便和潛在危險病原體的微小液滴噴射到周圍環境中。 但目前尚不清楚這種骯髒的變化究竟是如何進行的。

現在，這項新研究是首批深入這些渾水的研究之一。 雷射光設備讓團隊不僅可以看到羽流並觀察其形狀隨時間的變化，還可以計算和測量空氣中顆粒的噴發速度。

這是背景——所有令人不安的氣溶膠作用都始於沖洗。在北美的公共廁所，沖水器由沖洗閥提供動力，這是一種機械分流器，無需水箱即可排空和換水。如果你在美國的機場、學校或購物中心做過生意，你就會看到這些東西。

沖洗閥會將廁間前使用者離開時可見的痕跡衝入管道。但是那些能讓我們生病的看不見的東西呢？

SARS-CoV-2 和困難梭狀芽孢桿菌 (Clostridium difficile) 等病毒和細菌可以透過從屁股到廁所再到肺部的氣溶膠傳播。即使馬桶水裡沒有尿液或糞便，它也可能含有退伍軍人症病菌 ( Legionella)，它會導致嚴重的肺部感染。

「在將受污染的糞便放入馬桶後，經過數十次沖水，馬桶中的碗水含有較高水平的病原體」，Crimaldi 說。 通過仔細研究這些公共羽流，研究人員可以幫助減輕廁所相關疾病的傳播。

 

如果沒有適當的緩解措施，像 SARS-CoV-2 這樣的病毒會從廁所搭便車到你的肺部。圖片：Shutterstock

 

為什麼它很重要——最近的實驗強調了粒子可以傳播、停留和傳播疾病的距離。「眼見為實」，俄克拉荷馬大學健康科學中心的工業衛生學家和環境健康科學家 Evan Floyd 說，他沒有參與這項新研究。 畢竟，知識更豐富的公眾可以成為更健康的公眾。「這真的很重要，而且可能有很多價值」。

根據 Crimaldi 的說法，這些發現還可以指導廁所設計、廁所操作、管道甚至通風的改變，並改善學校、辦公室和醫院等擁擠建築的衛生條件，潛在的致命病原體可能會在這些地方迅速傳播。

你可能會想：為什麼公共廁所不能有個蓋子？ 沖水前蓋上蓋子確實可以顯著減少馬桶的羽流。 但是，多增加一個表面進行消毒——多一個供人們接觸的表面——會增加糞口傳播的風險。

弗洛伊德說：「沿途有人做出決定，認為糞口接觸傳播之危害比馬桶沖洗氣溶膠的風險和費用更大」。「但坦率地說，很長一段時間以來，人們真的不相信有多少馬桶沖水氣溶膠。 只是在過去 10 年左右，它才變得越來越被接受」。

到目前為止，我們對沖洗羽流的物理學知識仍然很粗糙。 近年來，科學家們報導了液滴的高速視頻和相關物理的計算機模擬。 但是，既沒有可視化也沒有量化最微小的馬桶顆粒所發生的事情。

他們做了什麼——Crimaldi 的實驗室使用沖洗閥供電的商用馬桶，尋求全面了解馬桶羽流（不包括常見的排泄物）。 5 納秒 ［納秒 (ns) 是國際單位制 (SI) 中的時間單位，等於十億分之一秒，即 1⁄1 000 000 000 秒，或 10−9 秒］長的雷射光脈衝每 100 毫秒左右發射一次，有點像綠色閃光燈。

科學家們透過在沖洗後每隔幾秒拍攝被照亮的氣溶膠圖像來測量羽流的形狀如何隨時間演變。

 

Crimaldi 和他的同事創建了一個精心設計的實驗室裝置來追踪馬桶水顆粒的軌跡。圖片：科羅拉多大學波德分校

 

相機捕捉到的每個雷射光脈衝都提供了氣溶膠的凍結框架，他們可以用一種特殊的算法對其進行分析，以勾勒出整個羽流中的粒子速度。

他們注意到羽狀物迅速上升並返回到馬桶後面的牆壁。顆粒最密集的區域——可能含有最高濃度的病原體——在 5.5 秒內飆升至馬桶上方約 1 英尺處。在沖水後的 8 秒內，研究人員觀察到顆粒會上升約 5 英尺。「那是大多數人的呼吸區」，弗洛伊德說。

氣溶膠繼續擴散超過 60 秒。「大多數人沒有意識到到處都有細微顆粒」，弗洛伊德說。「能夠快速可視化真是太好了」。

事實上，弗洛伊德懷疑克里馬爾迪的粒子計數可能是保守的。 氣溶膠中的水會蒸發，因此團隊可能會隨著時間的推移測量到較低的強度。 但實際上，他說：「所有的固體都還在那裡。 所以就像 COVID 一樣，你可能會有這些直徑為 2 到 10 微米的呼吸道飛沫顆粒」。

「固體會隨風而去」，他繼續說道，甚至在隔間外。通風將顆粒推向四周。打開隔間門並行走會產生使氣溶膠循環的渦流。「細小氣溶膠的真正問題在於，除了吸收所有空氣並將其透過清潔機制之外，沒有真正好的方法可以去除它們」。

 

紫外線可用於對充滿病原體的浴室進行消毒。圖片來源：Shutterstock

下一步是什麼——Crimaldi 希望隨著公眾對廁所羽流強度的接受，工業衛生將會得到改善。 為了提高浴室衛生，可以在羽流上方增加通風。 也許還有一些紫外線消毒，或者稱為靜電除塵器的小發明，可以去除帶電荷的顆粒。

該團隊尚未在馬桶中重複他們的糞便實驗，但 Crimaldi 對基於雷射光的可視化方法持樂觀態度。 「這為我們提供了一種能夠測試新馬桶設計的工具」，他說。 他想像工程師在集思廣益未來的商用廁所概念時，可以修改水壓、沖洗強度和馬桶形狀等變量。 展望未來，這項研究可以為他們提供一個基線來比較他們的工作。

重新設計可能會很棘手，因為改變每個元素可能會降低廁所的效率或它們現在擅長的事情的有效性，但 Crimaldi 堅持認為解決羽流危害至關重要：「看看影像」，他開玩笑說。 「這不可能更糟」。

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WATCH: NEW LASER EXPERIMENT REVEALS HOW HIGH POOP PARTICLES MAY BLAST AFTER WE FLUSH

A never-before-seen look at bathroom physics.

MAX G. LEVY / Nature

 

John Crimaldi

THIS SUMMER, IN Boulder, Colorado, John Crimaldi and his team of civil and environmental engineers gathered around a toilet — for science.

They positioned a laser to beam green light above the lidless bowl: If any normally invisible particles emerged as the toilet flushed, they hypothesized, they would scatter the light and appear as green dots. To record the potty dynamics, the team rigged up a camera a few feet away. Then … flush.

What happened next silenced the researchers. “We were all just stunned,” recalls Crimaldi. “We saw this incredibly energetic jet of particles shooting up towards the ceiling.”

Their laser caught a cloud, or plume, of particles flying into the air — then lingering there. “People just started laughing. They were like, ‘Oh, my God, you’ve got to be kidding me. That’s what happens when you flush the toilet?’”

Scientists focused a laser on a toilet to reveal just how far the potty particles can travel.CU Boulder

WHAT’S NEW — In a study published today in Scientific Reports, Crimaldi’s team from the University of Colorado describes how their laser-based rig visualizes lidless toilet plumes in more detail than ever seen before.

Scientists who study invisible airborne particles have reported for over a decade that lidless public toilets can eject tiny droplets that contain urine, feces, and potentially dangerous pathogens into the surrounding environment. But it’s not clear how exactly how this dirty exchange goes down.

Now, this new study is among the first to dive into those muddy waters. The laser rig allowed the team to not only see the plume and watch its shape evolve with time, but also to count and measure the speed of erupting airborne particles.

HERE’S THE BACKGROUND — All the unsettling aerosol action begins with a flush. In North America’s public restrooms, flushes are powered by a flushometer, a mechanical diverter that evacuates and replaces water without a tank. If you’ve done your business in an American airport, school, or mall, you’ve seen these things.

A flushometer will yeet the visible evidence of the stall’s previous occupant away into the pipes. But what about the invisible stuff that can make us sick?

Viruses and bacteria, such as SARS-CoV-2 and Clostridium difficile, can spread via aerosols that travel from butt to toilet to lung. Even if the toilet water holds no urine or feces, it might contain Legionella, which can cause severe lung infections.

“The bowl water in a toilet contains elevated levels of pathogens for dozens of flushes after that contaminated feces was put in there,” Crimaldi says. By studying these public plumes in close detail, researchers could help mitigate the spread of toilet-derived diseases.

 

Without proper mitigation, viruses like SARS-CoV-2 can hitch a ride from the toilet to your lungs.Shutterstock

WHY IT MATTERS — The recent experiment highlights just how far the particles may travel, hang around, and wreak illness. “Seeing is believing,” says Evan Floyd, an industrial hygienist and environmental health scientist at the University of Oklahoma Health Science Center who wasn’t involved in the new study. After all, a more knowledgeable public can be a healthier public. “That’s really important, and there’s probably a lot of value to that.”

These findings could also guide changes in toilet design, toilet operation, plumbing, or even ventilation, according to Crimaldi, and improve sanitation in crowded buildings like schools, offices, and hospitals, where potentially fatal pathogens can quickly spread.

You may wonder: Why can’t public toilets just have lids? Closing the lid before flushing does reduce a toilet’s plume significantly. But adding one more surface to sanitize — one more surface for people to touch — increases the risk of fecal-oral transmission.

“Somebody along the way has made the decision that the fecal-oral contact hazard was a greater risk and expense than toilet flush aerosol,” Floyd says. “But frankly, people really haven’t believed that there’s much toilet flush aerosol for a long time. It’s only in the past 10 years or so that it’s becoming more accepted.”

So far, our grasp of the physics of flush plumes remains crude. In recent years, scientists have reported high-speed video of droplets and computer simulations of the physics involved. But neither visualize nor quantify what’s happening with the tiniest of toilet particles.

WHAT THEY DID — Using a flushometer-powered commercial toilet, Crimaldi’s lab sought a comprehensive view of toilet plumes (sans the usual excrement). The 5-nanosecond-long laser pulses blasted every 100 milliseconds or so, somewhat like a green strobe.

The scientists measured how the shape of the plume evolved over time by snapping images of the illuminated aerosols every few seconds after flushing.

 

Crimaldi and his colleagues created an elaborate lab set-up to track the trajectory of toilet water particles.CU Boulder

Each laser pulse captured by the camera provided a freeze frame of aerosols, which they could analyze with a special algorithm to sketch out the particle velocities throughout the plume.

They noticed that the plume quickly shot up and back toward the wall behind the toilet. The densest region of particles — which would likely contain the highest concentration of pathogens — surged about a foot above the toilet bowl within 5.5 seconds. Within 8 seconds of a flush, the researchers observed that particles shot up about 5 feet. “That’s in most people’s breathing zone,” Floyd says.

Aerosols continued to spread over 60 seconds. “Most people don’t realize there are fine particles everywhere,” Floyd says. “It’s nice to have the quick visualization.”

In fact, Floyd suspects Crimaldi’s particle count might be conservative. Water from aerosols will evaporate, so the team likely measured less intensity over time. But in practice, he says: “All the solids are still there. So just like with COVID, you might have these respiratory droplets that are 2 to 10 microns in diameter.”

“The solids just go wherever the wind will push them,” he continues, even outside of the stall. Ventilation pushes particles around. Opening the stall door and walking create eddies that circulate aerosols. “The real problem with fine aerosol is there’s no real good way to remove them outside of taking all of that air and passing it through a cleaning mechanism.”

 

UV light could be used to disinfect pathogen-ridden bathrooms.Shutterstock

WHAT’S NEXT — Crimaldi hopes that as the public comes to terms with the intensity of toilet plumes, industrial hygiene will improve. To boost bathroom sanitation, ventilation can be added above the plume. Maybe some UV disinfection, too, or gizmos called electrostatic precipitators that remove particles with an electric charge.

The team hasn’t repeated their experiment with excrement in the bowl, but Crimaldi is optimistic about the laser-based visualization method. “This gives us a tool for being able to test new toilet designs,” he says. He imagines that engineers could tinker with variables like water pressure, flush intensity, and bowl shape when brainstorming future commercial toilet concepts. Moving forward, this study can offer them a baseline with which to compare their work.

Redesigns may be tricky since changing each element could make toilets less efficient or effective at what they do well now, but Crimaldi maintains that it will be critical to address the plume hazard: “Look at the video,” he jokes. “It couldn’t possibly be worse.”