If My Hand Set On Fire, Would It Hurt?

I don’t actually remember where this question came from, or why my son asked it. I mean, I suspect it was inspired by playing a video game. Or maybe from watching cartoons. I just have “If my hand set on fire, would it hurt? How bad?” in my notes, with no context whatsoever.

That happens, sometimes. I’ve got a bunch of questions I jotted down, and many of them lack context. But, in this case, it makes a fun follow-up to my last article.

Sources of burns

To start answering his question, let’s start with how you can get burned. More things than just fire can burn you, after all – just ask your skin, after a day at the pool without sunscreen. In fact, the John Hopkins Medical Library provides four different sources of burns:

  • Thermal burns. These burns are due to heat sources which raise the temperature of the skin and tissues and cause tissue cell death or charring. Hot metals, scalding liquids, steam, and flames, when coming into contact with the skin, can cause thermal burns.
  • Radiation burns. These burns are due to prolonged exposure to ultraviolet rays of the sun, or to other sources of radiation such as X-ray.
  • Chemical burns. These burns are due to strong acids, alkalies, detergents, or solvents coming into contact with the skin or eyes.
  • Electrical burns. These burns are from electrical current, either alternating current (AC) or direct current (DC).

So, if my son’s hand was to be set on fire, he’d experience a thermal burn. Alternately, if he got a sunburn he’d have a radiation burn, if he poured lye on his hand he’d have a chemical burn, and if he stuck his finger in a live lightbulb socket he’d get an electrical burn. He’d also have parents doing their best to stay calm until he was taken care of, but that leads into an entirely different question of the “would you still love me if I did something stupid?” type.

(For the record, he’s never actually asked that question. But the answer is: “Yes, I would. I might not be happy with your behavior, but I’d still love you. Now take your fingers away from that electrical socket.”)

Ultimately, each of these sources of burns has some unique characteristics. But they all have the same basic effects.

Let’s talk about skin

Your skin has three layers: the epidermis, the dermis, and the hyodermis. The epidermis is the outer layer, composed of four to five layers of skin cells that protect the underlying layers. These cells manufacture and store keratin, a tough and fibrous protein that also (in a slightly different form) makes up our fingernails and hair and the horns of a rhinoceros. The epidermis also contains the skin pigment melanin, meaning that much of our conceptions of race aren’t even skin deep. The living layers of the epidermis are covered with layers of dead, keratinized cells that flake off over time. Beneath the epidermis is the dermis, two layers of connective tissue that contain blood and lymph vessels, nerves, hair follicles, sweat glands, and other structures. Finally, the hypodermis is connective tissue filled with more blood vessels and subcutaneous fat that serves to connect the skin to the bones and muscles.

“Solid burn, Branch.”

Returning to the John Hopkins Health Library, we learn that there are three classifications of burns – and you’ve probably heard what they are: first-degree, second-degree, and third-degree. Each of these relates to how deep the burn penetrates into the skin. First-degree burns are also referred to as superficial burns, and only affect the epidermis. It’ll be red and painful, dry to the touch, and lacking blisters.

Second-degree burns are also referred to as partial thickness burns, and both the epidermis and dermis are damaged. The skin will still appear read, but it is likely to be blistered and swollen.

Third-degree burns are also called full thickness burns, and this is where it gets really bad. The hypodermis is also damaged in a third-degree burn, and parts of the body below the hypodermis may also be involved. Parts like muscles, tendons, and bones (some sources call this a fourth-degree burn when this occurs). Third-degree burns will look whie or charred, and there tends to be no feeling in the burn site. Why? because the nerves have been destroyed.

Burns are further classified by burn percentage, which estimates the total area of the body affected by the burn. This is done on a “rule of nines”, in which body coverage is estimated in multiples of 9.

The chart doesn’t call out a hand specifically, but it would probably be considered 4.5%.

How much would it hurt?

There are a number of pain scales. The one I found first, and will be using as an example, ranks from 1-10 (well, technically 0-10, but 0 is “No pain. feeling perfectly normal.”). So, here’s the levels:

  1. Very light barely noticeable pain, like a mosquito bite or a poison ivy itch. Most of the time you never think about the pain.
  2. Minor pain, like lightly pinching the fold of skin between the thumb and first finger with the other hand, using the fingernails. Note that people react differently to this selftest
  3. Very noticeable pain, like an accidental cut, a blow to the nose causing a bloody nose, or a doctor giving you an injection. The pain is not so strong that you cannot get used to it. Eventually, most of the time you don’t notice the pain. You have adapted to it.
  4. Strong, deep pain, like an average toothache, the initial pain from a bee sting, or minor trauma to part of the body, such as stubbing your toe real hard. So strong you notice the pain all the time and cannot completely adapt. This pain level can be simulated by pinching the fold of skin between the thumb and first finger with the other hand, using the fingernails, and squeezing real hard. Note how the simulated pain is initially piercing but becomes dull after that.
  5. Strong, deep, piercing pain, such as a sprained ankle when you stand on it wrong or mild back pain. Not only do you notice the pain all the time, you are now so preoccupied with managing it that you normal lifestyle is curtailed. Temporary personality disorders are frequent.
  6. Strong, deep, piercing pain so strong it seems to partially dominate your senses, causing you to think somewhat unclearly. At this point you begin to have trouble holding a job or maintaining normal social relationships. Comparable to a bad non-migraine headache combined with several bee stings, or a bad back pain.
  7. Same as 6 except the pain completely dominates your senses, causing you to think unclearly about half the time. At this point you are effectively disabled and frequently cannot live alone. Comparable to an average migraine headache.
  8. Pain so intense you can no longer think clearly at all, and have often undergone severe personality change if the pain has been present for a long time. Suicide is frequently contemplated and sometimes tried. Comparable to childbirth or a real bad migraine headache.
  9. Pain so intense you cannot tolerate it and demand pain killers or surgery, no matter what the side effects or risk. If this doesn’t work, suicide is frequent since there is no more joy in life whatsoever. Comparable to throat cancer.
  10. Pain so intense you will go unconscious shortly. Most people have never experienced this level of pain. Those who have suffered a severe accident, such as a crushed hand, and lost consciousness as a result of the pain and not blood loss, have experienced level 10.

I couldn’t find any pain chart rankings for burn pain, partially because pain is a subjective (although real) phenomena. The Chicago Clinic explains, however, that

Burn pain can be one of the most intense and prolonged types of pain. Burn pain is difficult to control because of its unique characteristics, its changing patterns, and its various components. In addition, there is pain involved in the treatment of burns as the wounds must be cleansed and the dressings changed. Studies have concluded that the management of burn pain can be inadequate, and such studies have advocated more aggressive treatments for pain resulting from burns. Lastly, some burns can be mentally traumatic and/or physically disfiguring and lead to psychological pain that must be addressed, as well.

So there’s that.

What Are Vocal Cords?

“Dad?” my son asks. “Why does Darth Vader sound funny?”

We’re sitting on the couch when he asks the question. I’m reading, and he’s playing with his Legos, and the question doesn’t come from as far out of left field as it might seem. The majority of his Legos are Star Wars themed, after all. “Because the people who made the movie wanted him to sound scary,” I say.

“No,” he huffs. “I mean, in the movie!”

“Oh,” I say. “Well, his vocal cords got hurt when he fought Obi Wan.”

“Vocal chords?” he asks, sounding baffled. “What are vocal chords?”

What Indeed?

I don’t know, to be honest. Oh, sure, I know they’re the things in your throat that vibrate when you talk, and that they’re the things that actually let you speak. But I have no idea beyond that. The name always made me imagine a set of fleshy guitar strings stretched across my throat – when I thought about it at all – but I’m fairly confident that this isn’t correct. So, let’s look into the answer. Literally.

Vocal Cords

Those are vocal cords – also known as vocal folds – in action. Medscape describes them as “mucous membrane infoldings that stretch horizontally across the middle laryngeal cavity. They are attached anteriorly at the angle on the interior surface of the thyroid cartilage and project posteriorly to the arytenoid cartilages on either side.” They’re found within the larynx, at the top of the trachea, and open when inhaling and close when swallowing. They also close to help vibrate and modulate air expelled from the lungs to enable us to produce sounds (like, for instance, speech).

illu_larynx

Technically, there are two sets of vocal cords. The “true vocal cords” (or vocal folds) and the “false vocal cords” (or vestibular folds). These vestibular folds primarily serve to protect the more delicate vocal folds, but may also be “used in the production of deep tones and screaming or throat singing”. So, if you happen to enjoy black metal or Tuvan or Mongolian throat singing, you have heard and appreciated the false vocal cords.

On average, adults have larger vocal cords than children and men have larger vocal cords than women. This is why, again on average, adults have deeper voices than children and men have deeper voices than women. Larger vocal cords vibreate more slowly and with a longer frequency, creating lower sounds. Women are also more likely to have vocal folds that appear to be a pearly white, while men are more likely to have pinkish vocal cords.

Human are not born with fully developed vocal folds. Infants lack a vocal ligament, which allows the muscles of the larynx to easily control the vocal folds. “The vocal ligament begins to appear at about 4 years of age. The formation of the 3 defined lamina propria layers occurs between the ages of 6 and 12 and are fully mature at the end of adolescence.”

Care to tie this back to Star Wars?

Of course I would, because that’s what spawned this question. Clearly, the vocal cords can be damaged – acid reflux and smoking can thicken them, and significant use can stiffen them. Stiff vocal cords don’t vibrate as well, reducing vocal range and making speech difficult. Surgeons can repair this stiffness by replacing the vocal cords with synthetic materials. Specifically, a variation of polyethylene glycol called PEG30, which mimics the flexibility of human vocal cords and moves in a very similar manner to the natural tissues that compose them. So, instead of having a raspy mechanical voice, Darth Vader could have been given an amazing singing voice.

Not that the Dark Lord of the Sith doesn’t rock out anyway.

There’s Creepy Stuff In My Ears!

Not too long ago, we had to clean my son’s ears out. When I was a child, this involved q-tips. There have been all kinds of advances since then, though, and now we use drops that get flushed out with warm water.

My son hated it. Not because it hurt, mind. But he had to lay down for a full minute per ear, with a washcloth on his ear, and he was bored. Then, after we rinsed out the ear, he looked at what came out. “There’s creepy stuff in my ear!” he said.

“That’s just ear wax,” I told him.

“What’s ear wax?”

Uhm…

Seriously? Last week wasn’t enough for you?

Look. Ear wax is a fact of life. I have it, you have it, famous actors and supermodels have it. Everyone has it. But, how many of us know what it actually is or what it is for? I sure don’t. And I promised my son I’d answer his questions. So, we’re going to start with glands.

Glands

Your skin has glands, which are organs that synthesize some substance and then release that substance for use by the body. Chief among them are the sebaceous glands, found everywhere on your skin except for the hands and the soles of the feet. These sebaceous glands secrete an oily or waxy substance called sebum, which lubricates and waterproofs your skin. Sebum is also slightly acidic, and helps serve as a barrier to viruses and bacteria.

howdowehear

Along with sebaceous glands, the outer third of your ear contains ceruminous glands. These glands produce cerumen, which helps you hear by keeping your eardrum pliable. It also helps keep the external auditory canal clean, and serves as another barrier to bacteria and foreign particles.

Earwax

Earwax is a mixture of sebum and cerumen and all the things block and trap: dirt, bacteria, shed hair and skin cells, and so on. People of African and European origin are likely to have wetter cerumen (and wetter, dark brown earwax), while Asians and Native Americans will have dryer cerumen (and dryer, grey or yellow earwax).

Normally, earwax helps to clean the ear canal by a process of “epithelial migration”. Cells in the ear canal are pushed outwards by the growth of new cells, and earwax – being sticky – clings to the cerumen and sebum produced by the glands and moves with the cells. Eventually it is pushed to the outside of the ear and out, taking dead skin cells and dirt and bacteria with it.

Excess Earwax and Blockages

According to the Mayo Clinic, excess earwax is caused by the ear secreting excess ebum and cerumen. Or, in other words, excess earwax is caused by excess earwax. Go figure. If you have excess earwax, it can be softened with a few drops of mineral oil or hydrogen peroxide, and then – after softening for a day or so – rinsed out (gently) with warm water. They recommend that you never attempt to dig it out, as that can push the wax deeper and block the ear canal or even damage the eardrum. If you can’t clean it out yourself, you should see a doctor.

Why Do We Get Boogers?

It’s winter, and the temperature has been really strange. Up and down, up and down. One day I can walk around outside, thinking my light jacket is too much coat. Two days later, it’s snowing. It’s been that kind of season, and I think that’s why my son has the sniffles. He’s not sick, per se, but he’s sniffling and sneezing and his nose is running. So recently, he goes and grabs a tissue and wipes his nose. “Dad,” he asks, “why do we get boogers?”

Well, I did say I’d answer his questions…

the-nose

What is a booger?

Let’s be honest here. You know what a booger is. You were a kid once, even if you haven’t been around any recently. Still, let’s do this right. Merriam-Webster gives two different definitions for the word “booger“:

  1. Bogeyman
  2. a piece of dried nasal mucus.

Clearly, in the contex of my son’s question, we’re talking about the second definition. I’ve never told him about the “bogeyman”, and I don’t think any of his friends have told him about that character. He’s six, and he’s feeling scared of the dark, so I think it would have come up if he had. So, let’s focus on the dried nasal mucus. The Online Etymology Dictionary gives the following explanation for the word

“nasal mucus,” by 1890s; earlier bugger. Also boogie.

So, yeah. No Greek or Latin or Proto-Indo-European here.

What is mucus?

Going back to Merriam-Webster, mucus is defined as “a viscid slippery secretion that is usually rich in mucins and is produced by mucous membranes which it moistens and protects”. It’s a fairly common fluid produced by the human body – heck, by nearly every animal, not just us humans. The respiratory system produces mucus in the nose, the airways (i.e. your sinuses and throat), and the lungs, as a way of trapping foreign particles. What foreign particles, you ask? Dirt. Dust. Bacteria. Pollen. Allergens. You name it, your mucus traps it. And the more your respiratory system needs to trap, the more mucus it produces. That’s why you generate more mucus (and then cough) when you get exposed to allergens or you get sick. Your body is trying to trap more of the foreign particles and expel them before they can cause you more problems.

Your respiratory system isn’t the only place that makes use of mucus, however. Your digestive system uses it for the whole length – from the esophagus into the stomach and the intestines and into the colon – as a way of lubricating your food in its journey through your body. It also shows up in the reproductive system, functioning as a lubricant and a means of transporting sperm and eggs through the body. Your eyes generate mucus as well, lubricating and protecting sensitive cells and keeping them moist.

So. How does mucous become boogers?

Bear in mind that mucus isn’t just water. It’s full of proteins and antibodies (because it isn’t just a passive defense) and electrolytes, not to mention all the dust and dirt and bacteria and such that it has trapped. As the water in the mucus evaporates or gets absorbed by the body, these solids get left behind, sticking and clumping together until – if not disturbed – they form masses of noticeable size.

I can’t believe I’m going to ask this, but… why the nose? Why not eye boogers?

Actually, those can happen. Eye crust, also known as rheum, is essentially eye boogers.

Great. Anything else?

Yeah. You know how your mom said you shouldn’t pick your nose and eat it?

Do I want to know this?

Hey, you’re the one still reading.

It turns out that there’s a hypothesis that boogers have a sugary taste that is meant to entice you to eat them. Because the act of doing so helps introduce weakened pathogens from the environment to your immune system, building up your defenses. This is rather controversial (not to mention nauseating), and it has not been tested. A number of scientists als point out that you swallow mucus all the time, just by living. This still serves to introduce the pathogens to your body. So don’t take this as a license to go to town on your nose, please.

I wasn’t planning to. Also, I hate you so very, very much right now.

Look, the human body is endlessly fascinating. Even the bits that we find culturally repugnant. Besides, you’re the one reading the article about boogers. What did you expect?

A Little More On The Purple Eye

The day I posted “Do I Have A Purple Eye?“, a friend of mine made the following comment on Facebook:

Aha! You, sir, are incorrect. You forgot cerebral contusions which don’t leak into skin tissues but into surrounding brain tissue.

Well, this got my attention (and made my skin crawl). More importantly, it got me looking deeper into this whole ‘contusion’ thing. Buckle in, folks: this will be uncomfortable.

Not all hematomas are created equal

To begin with we’ll need to revisit some definitions, because I wasn’t entirely correct. Broadly speaking all bruises are hematomas, but not all hematomas are bruises. This is because a hematoma is just (“just”) a collection of blood outside the blood vessels, which can be caused by trauma, illness, or just the blood vessel tearing from weakness. Contusions are a specific subset of hematoma caused by blunt trauma.

black-eye

According to Wikipedia, hematomas come in several flavors. These include:

  • Subdermal, which is a hematoma beneath the skin.
  • Skull/brain, which are hematomas where blood pools either within the brain itself or in the cerebrospinal fluid that cushions your brain within your skull. Subdermal hematomas of the scalp also get classified as skull/brain hematomas.
  • Breast, which is a hematoma within the breast tissue – meaning that women are much more prone to these than men.
  • Myocardial, which is a hematoma in your heart muscles.
  • Pulmonary, which is a hematoma in your lung tissue.
  • Subconjunctival, which is a hematoma of the conjunctiva – the tissue that lines the inside of your eyelid and covers the whites of your eyes.
  • Perichondral, which is a hematoma of the ear. Specifically, it is blood pooling in such a way that the ear cartilige seperates from the perichondrium (the connective tissue that surrounds the cartilige of developing bone). This is where so-called “cauliflower ear[https://en.wikipedia.org/wiki/Cauliflower_ear]” comes from.
  • Perianal, which is a hematoma of the anus. This is also known as a hemorrhoid.
  • Subungual, which is a hematoma beneath a fingernail or toenail, and is sometimes known by names such as “runner’s toe” or “skier’s toe”.

Hematomas are also classified by degree. A petechiae is less than 3 mm in diameter, a purpura (which I mistakenly thought was a type of hematoma, instead of a degree) is between 3 mm and 1 cm in diameter, and an ecchymosis is larger than 1 cm in diameter. So a petechiae subdermal hematoma is a tiny thing on your skin, while a perianal ecchymosis is no diagnosis you ever want to have.

Now, a contusion is just (just?) a hematoma caused by our old friend blunt force trauma. So, really, any type of hematoma can be a contusion. Myocardial contusion? Sure. Perianal contusion? Yep. Perichondral ecchymosic contusion? Why not.

So there you have it. Anything that has blood vessels in or near it can suffer a hematoma. Skin, heart, lungs, eyes, whatever.  And now I’m going to pack myself in cotton for a while.  Just until the skin crawling and the paranoia wears off.

Do I Have A Purple Eye?

My son has a wooden toy axe that he bought with his allowance money when we went to the Ohio Renaissance Festival. This will be an important fact, momentarily.

Last week, we were roughhousing in his room. That ridiculous sort of “wrestling” you do with your kids, that’s mostly the kid jumping on you and climbing all over you and laughing hysterically. Both of us were having a good time, even though I had to remind him that he shouldn’t actually hit me with the axe. He tells me he’s sorry, then jumps on my back and slides around and goes face-first onto the floor. I’m not concerned, because he does this about once a minute when we’re roughhousing.

Then he shouts “ouch!”

Being a dad who tries hard to be a good dad, I immediately check to see what’s going on. He has, it seems, landed face first not on the floor but on the axe handle. When he comes up, he’s rubbing his eye. Then he moves his hand. “Do I have a purple eye?” he asks.

I look. “No. You’re all right.”

He nods, rubs his eye one last time, and then tackles me.

What is a bruise?

Clearly, he didn’t get significantly hurt. The pain went away quickly, and no bruising developed. But that got me thinking. I’ve had bruises before, but I’ve never really been sure what they are. I know they’re caused by impacts, and I’m pretty sure they involve bleeding beneath the skin, but that hits the limits of my knowledge. So even though he didn’t ask a direct question along the lines of “what’s a bruise?”, I decided to look into the question.

Advanced Tissue defines a bruise as “a condition in which small blood vessels under the skin rupture, causing blood to leak into the underlying skin tissue.” Which makes me feel good, finding out that my received wisdom (probably from my parents, but I couldn’t say for sure) is correct. But then the definition goes on to note that “there are three common types of bruises that can occur based on the severity of an injury: contusions, hematomas, and purpura.”

Now I’m intrigued. I’ve heard the word ‘contusion’ before, and just assumed it was a synonym for a ‘bruise’. I’ve also heard the word ‘hematoma’, and recognize just enough Latin to know that it must involve blood, but I don’t know what one is. And ‘purpura’? Well, let’s just say my first guess would have been “that’s the intermediate lifecycle state of a butterfly, right?”. And then I’d have acknowledged that I’m entirely wrong.

So, a contusion is the most common type of bruise, caused by “blunt force trauma” – that is, hitting yourself. If the impact is strong enough to damage blood vessels, a contusion forms. The skin under the impact site will turn colors; red at first, then black, blue or purple, then possibly green and yellow as the blood breaks down and is reabsorbed by the body.

a_bruise

A hematoma is ” a type of bruising where a massive collection of blood has pooled at the injury site”, and is often accompanied by greater pain and swelling. They can be caused by the ever-popular ‘blunt force trauma’, by spontaneous rupturing of blood vessels (and I’m just a little on edge knowing that “spontaneous rupturing of blood vessels” is a thing), or by surgical procedures. They can be dangerous if they occur in or near vital organs.

Purpura are smallish bruises, generally resembling purple-colored patches or spots – that occur when small blood vessels rupture. Most frequently, these aren’t caused by our good friend blunt force trauma; they are typically the result of certain diseases, aging (which makes the blood vessels more fragile), and some drugs that reduce platelet count. Why that latter? Because platelets are instrumental in the clotting process, which helps seal damaged vessels. If they’re slow to seal a small rupture in a small vessel, for example because the platelet count is low, a purpura forms.

How do you treat a bruise?

Generally, bruising is initially treated with the “RICE method”. RICE, in this context, is an acronym that stands for Rest, Ice, Compression, and Elevation. For the first 24 to 48 hours you should take it easy on the injured area, put ice and pressure on it (to reduce swelling), and keep it elevated if at all possible (which reduces the blood flow, which also reduces swelling). After that initial 24 to 48 hour period, light to moderate exercise of the muscles and joints near the bruise will help with healing. And be certain to consult with your doctor if it seems especially severe or painful, or if it doesn’t seem to be healing. I’m a stock broker, not a doctor. Don’t depend on me for your health care, please.

Oh, and there’s this statement from Advanced Tissue: “Unlike contusions and hematomas, purpura treatment will vary on a case-by-case basis as determined by a medical professional by evaluating the underlying cause of the purpura.”

Wait… bone bruise?

Yes, I know that I didn’t actually say anything about the hideous-sounding ‘bone bruise’. But it came up in the “Treating a Wound or Bruise” information I was reviewing. The very phrase makes me cringe and makes my skin crawl, so I now have a powerful need to find out what it is in hopes of reducing that reaction. I’m weird that way – as a child, I had to watch my doctor give me shots and draw blood in order to reduce my fear of getting stuck with a needle, too.

Physopedia defines a bone bruise as:

Bone bruise is one of the four types of fractures that occur in the human body, the others are: stress fractures, osteochondral fractures and bone fractures.

Bone bruise is a term that contains 3 different kinds of bone injuries: sub-periosteal hematoma, inter-osseous bruising and sub-chondral lesion.

A bone bruise can be described as a stage before the fracture.

When we speak of a real bone fracture it means that all the bone trabeculae of that specific place are fractured. In case of a bone bruise only a few of the trabeculae are broken.

None of that is reducing my urge to cringe. Let’s dig deeper.

The periosteum is the layer of connective tissue that covers a bone. If you’ve ever gnawed on a chicken leg or pork chop bone, and found yourself stripping off a thin transparent layer from the bone, that’s the periosteum. (Please tell me I’m not the only one who’s ever done that…) It’s actually two layers. The outer layer is tough collagen and fibroblasts (which produce more collagen), and the inner layer is stem cells and osteoblasts (which help repare the hard part of the bone if its damaged). So, that first type of bone bruise – the sub-periosteal hematoma – is caused by rupturing the blood vessels immediately beneath the periosteum – hence the name. This type of bone bruise is the direct result of our old friend blunt force trauma.

Inter-osseous bruising, the second form of bone bruise, is damage to the blood vessels that penetrate the bone itself. why do we have blood vessels penetrating our bones, you ask? Because our bones contain marrow, a spongy cellular factory for new blood cells. Which makes marrow extremely important, as you may guess, and which also means that we need a way to move them out. Well, “repetitive high compressive force on the bone (extreme pressure on regular base)” can rupture those vessels, causing blood to pool inside the bone itself. Yes, my skin is crawling again.

Sub-chondral lesions are bone bruises that occur beneath the cartilage layer of a joint – the padding that protects bone where it meets other bone. “The main trigger is an extreme compressive force that literally crushes the cells, that results in a separation of the cartilage (or ligament) and the underlying bone, plus bleeding when the energy of the impact extends into the bone. The other trigger is a shearing force, it sustains from a rotational mechanism such as twisting and translational forces. These will also cause that the cartilage tissue will be stripped away and exposing the underlying bone. It results in the same injury as a compressive force injury but this is another source of the injury.”

Yeah. Not better.

Bone bruises don’t show up on x-rays unless there is an associated fracture, so diagnosis can be difficult. Treatment generally involves rest and avoiding repetitive and strong loads on the bruised bone, and plenty of rest. You should really see your doctor, if you think you have one of these.

Can They Hear Me In China?

“BOO!” my son yells, leaping out from a shrub.  And then he dissolves into a fit of laughter.

This is a game he likes to play, whenever he gets the chance.  As soon as we’d parked and he got out of the car, he ran up the sidewalk towards the front door of our condo.  And then he ducked back behind the hedge, lurking.  The game, now, is for me to walk towards the door.  Then he’ll jump out and shout “boo” and try to make me jump.

“Did you know I was there, daddy?” he asks.

Of course I did, I think.  You hide in the same place every time.  “Kind of,” I tell him.  “I guessed where you were.”

He blows that off.  “I was loud, wasn’t I?”

“Yes, you were,” I answer, unlocking the door.

“Was I loud enough for them to hear me in China?”

How Do We Hear?

Obviously, we hear with our ears.

howdowehear

Sound waves, which are really just pressure waves in the atmosphere, strike the outer ear and are channeled into the ear canal.  These pressure waves vibrate the eardrum, which in turn vibrates the bones of the inner ear (the malleus, the incus, and the stapes), amplifying the vibrations and transmitting them into the inner ear (or cochlea).  Hairs in the cochlea are stimulated by these vibrations, creating an electrical signal that transmits along the auditory nerve to the brain.

Yes, this is terribly simplified.

How Loud Are You?

Strictly speaking, “loud” is a matter of perception – the same pressure wave can result in different experiences of “loudness”.  However, this perception is tied to the intensity of the pressure wave, just as the perceived pitch of a sound is tied to the frequency of the wave.

wavy33b

A wave

Using the above image of a wave, the intensity is how high the peaks and how low the valley is – the higher the peak, the more intense the wave.  Another way to think of intensity is how much energy the wave carries – the taller the wave, the more energy (just like how bigger ocean waves hit harder than small ones).  Frequency, on the other hand, is how fast the wave moves – the closer together the peaks, the faster the wave moves and the higher the frequency.  Generally speaking, we perceive intensity as loudness (because the pressure wave hits the ear harder) and we perceive frequency as pitch (because the pressure wave stimulates the bones in the ear faster).

“Loudness” is measured in decibels (dB), because one decibel is the “just noticeable difference” in sound intensity for the human ear – assuming the pressure wave generated is in the 1,000 Hertz (Hz) to 5,000 Hz range we are best at hearing.  Every 10 dB represents multiplying the intensity of the pressure wave by 10 – that is, a 10 dB sound is 10 times more intense than a 0 dB sound, a 40 dB sound is 10,000 times more intense than a 0 dB sound, and a 100 dB sound is 10,000,000,000 times more intense than a 0 dB sound.

We generally can’t hear anything below 0 dB, and normally speak in the 60 to 65 dB range.  A jackhammer 50 feet away is about 95 dB, a power mower 3 feet away is around 107 dB, and loudness causes pain starting around 125 dB.  Sounds at 140 dB and greater can cause permanent damage with even short exposure.

How Far Away Can We Hear?

This gets tricky, because the answer is “no further than when the perceived volume falls to 0 dB”.  Tricky, because sound obeys the inverse square law which states that for any source power P generated at the center of a sphere, the intensity of at the surface of that sphere is P/4πr2 (although a good approximation is P/r2, since the math gets easier).  According to Hyperphysics, r is pretty much always measured in meters for these purposes (because sound intensity is actually measured in watts per meter squared, so it keeps the units the same).

Since sound intensity can be transformed into decibels, it’s really not a stretch to directly apply the inverse square law to decibel measurements.  So, a 60 decibel conversation would be perceived as 60 decibels at 1 meter away, 60/(2*2) = 15 decibels at 2 meters, 60/(3*3) = 6.6 decibels at 3 meters, 60/(4-4) = 3.75 decibels at 4 meters, less than 1 decibel at 8 meters, and so on.  Realistically, at this point, it’s probably safe to call it “inaudible” (even though you could technically detect it).

How Loud Would You Have To Be For Someone To Hear You In China?

All right, here’s where the math gets… entertaining.  I live in Cincinnati, Ohio, which is (according to Google) 10,969 kilometers from Beijing.  Measuring along the curved surface of the Earth, that is.  But, to keep things simple, we’ll ignore that.  So, 10,909 kilometers is 10,909,000 meters.  To be heard in Beijing, we’d have to generate enough decibels to result in a greater than 0 dB sound 10,909,000 meters away.

For laughs, let’s aim for a 60 dB sound.  That way, our sound can be clearly understood.  The radius is 10,969,000.  So, the equation looks like this:  x/10,969,0002 = 60.  Solving for x gives us x = 60(10,969,0002), or x = 7,219,137,660,000,000 dB.  This is a nonsensical level of perceived volume, and would render you deaf in ludicrously tiny fractions of a second.

What could generate that?  Well, we’d have to reverse engineer the decibels into watts of power, which converts to 721913765999988 watts per meter, or about 721.9 terawatts of power.  Now, you can roughly convert watts to Joules per second, so that’s roughly the explosion of a 200 kiloton nuclear weapon.

Assuming I did my math correctly, which I’m not guaranteeing.  What I can guarantee is that there is no way you’d want to be standing anywhere near something loud enough in Cincinnati that you can hear it in China.