Do you know about Supra locks? They are high-tech versions of the old combo locks we are all used to, and they have have a few advantages. They are opened by an electronic keypad that inspectors carry with them and they keep records of who accessed them and at what time. Combo locks are still common in many places but it seems that they are slowly being replaced by Supra Locks, which are generally considered to be superior. To find out more about the pros and cons of both types of lock boxes check our our new article on lock boxes for inspectors.
Water is essentially an incompressible solid. It has no latent heat energy within itself to expand when released, unless the water is superheated. Water above 212˚ F is superheated water, and superheated water would really like to turn into steam at atmospheric pressure. It possesses latent heat energy, which can flash into steam and create a force that is not unlike an explosion.
Water would normally boil at 212 ˚F, but inside a tank it can’t expand anywhere so it can’t boil off into steam. Water in a “closed” system and under pressure, such as inside a hot water tank, has a much higher boiling point. For example, where water supplied to a tank is at 50 psi, the boiling point is 297.7˚ F.
Let’s assume a water heater tank has 30 gallons of superheated water inside it. Assume 50 psi and the water temperature is superheated at 300 ˚F. Remember that superheated water really wants to turn into steam. If the tank ruptures, then 30 gallons of superheated water will instantaneously turn into steam in an outwards direction through the rupture.
There is a tremendous amount of energy released as the superheated water is exposed to atmospheric pressure and immediately turns into steam. Every cubic inch of water becomes a foot of steam!
Below is a list of energies developed in a 30-gallon hot water tank. The following data shows the explosive energy created in a 30 gallon hot water tank at various pressures and temperatures.
At 0 pressure psi, water will boil at 212 F, and the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure is 0.
At 10 pressure psi, water will boil at 239.5 F, and the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure is 479,800.
At 30 pressure psi, water will boil at 274.0 F, and the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure is 1,305,000.
At 50 pressure psi, water will boil at 297.7 F, and the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure is 2,021,900.
At 70 pressure psi, water will boil at 316.0 F, and the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure is 2,642,000.
At 90 pressure psi, water will boil at 331.2 F, and the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure is 3,138.400.
Note that at 50 psi, water flashes into steam at 297.7˚ F, and the energy released equals more than 2 million foot-pounds of energy, similar to the explosive energy released by one pound of Nitroglycerin. A 16-inch gun on a USS Iowa class battleship produced a 7,500,000 foot-pounds of energy.
Combination temperature and pressure relief (T & P Relief or TPR) valves do two things: 1) they open and release water out of the tank if the temperature exceeds 210˚F (just below the boiling point), and 2) they will open if the pressure in the tank exceeds 150 psi (the maximum normal operating pressure for a water heater.)
It is essential to avoid excessively high water temperatures and pressures at a water heater tank.
“How to Properly Inspect Hot Water Tanks” – An online video training course for property inspectors. https://www.nachi.org/advancedcourses.htm
- More decks collapse in the summer than in the rest of the year combined.
- Almost every deck collapse occurred while the decks were occupied or under a heavy snow load.
- There is no correlation between deck failure and whether the deck was built with or without a building permit.
- There is no correlation between deck failure and whether the deck was built by a homeowner or a professional contractor.
- There is a slight correlation between deck failure and the age of the deck.
- About 90% of deck collapses occurred as a result of the separation of the house and the deck ledger board, allowing the deck to swing away from the house. It is very rare for deck floor joists to break mid-span.
- Many more injuries are the result of rail failure, rather than complete deck collapse.
- Deck stairs are notorious for lacking graspable handrails.
- Many do-it-yourself homeowners, and even contractors, don’t believe that rail infill spacing codes apply to decks.
Ever have trouble finding a friend’s house because you can’t see any house numbers? Well, imagine how hard it is for paramedics and firefighters who are trying to save lives. House numbers that are missing or not clearly visible from the street are a serious public health issue. Fortunately, house numbers cost almost nothing and are easy to install. Many jurisdictions have begun fining residents who fail to display numbers clearly. To find out more inspection-related advice about this topic and why it’s so important, check out our new article on house numbers for inspectors.
There’s no such thing as a burglar-proof home but there are some things that homeowners can do to make their homes less appealing to potential thieves. Get a dog. Don’t want to? Put up “beware of dog” signs around the yard. Get an alarm system. Don’t want to? Put up alarm stickers anyway. The house should look like it is occupied even when it isn’t. Or, you can move to Norway – they barely have any break-ins. Just don’t go to Australia if you want to keep your home safe. Inspectors should learn these tips and statistics so they can pass them onto their clients. For more inforation, take a look at our new article on burglar resistant homes.
We are all used to seeing backflow preventers, even if we didn’t know what they were used for. These complicated assemblies of pipes are designed to prevent water from reversing its course and re-entering the public water supply. Water that has been polluted or contaminated and re-enters the potable water system is a serious public health threat. There are a number of different types, although only one is common in residences. To find out more, take a look at our new article on backflow preventers for inspectors.
You don’t often think about how dangerous garage doors can be, but tens of thousands of injuries happen every year as a result of defective components and misuse. Garage doors weigh hundreds of pounds and are held in place by springs under extremely high tension. As inspectors, you should know what to look for in garage doors to make sure that they are not creating a serious safety hazard, and also what to tell clients about ways they can stay safe. To find out more about this inspection area, take a look at our new article on garage doors and garage door openers.
Lead has been mined for thousands of years because it is common and possesses many properties that make it useful. Yet even in ancient times, it was known to cause terrible illnesses and contact with the metal was avoided. It’s surprising then that up until the 1950’s, paint was made of up to 50% lead and cars were allowed to burn leaded gasoline. Despite regulations that limit the amount of lead in homes, many older homes still have large amounts of the substance. To find out more about lead poisoning and where lead is found in homes, check out our new article on lead for inspectors.
Do you know the difference between a collar tie and a rafter tie? They may look similar, but they are used for very different things. Contrary to popular belief, collar ties are not capable of holding the walls together. They are simply too high up in the attic. Collar ties prevent uplift due to wind. Rafter ties are placed lower in the attic and to keep the walls from spreading due to the weight of the roof. They each have their own requirements and purposes, and inspectors should be ready to differentiate he two. To find out more, take a look at our new article on collar ties and rafter ties for inspectors.
Few bathrooms are installed with carpet, and for good reason – bathroom floors are exposed to urine and large amounts of moisture. Moisture can lead to the growth of mold, which can cause structural damage as well as health problems. Urine, well, we don’t need to go into that, but you know you don’t want to touch it. Carpet traps these things and makes them less obvious, so they don’t get cleaned as often. To find out more about the dangers associated with carpet installed in bathrooms, check out our new article on carpeted bathrooms for inspectors.