Some call me Tim?

By Timothy Allinson, P.E.,
Murray Co., Long Beach, Calif.

If you are a fan of Monty Python you might recognize this title quote as a line from The Holy Grail. It’s the scene where King Arthur and his knights stumble across a wizard with the gift of throwing fireballs to explode trees.

Arthur: What manner of man are you that can summon up fire without flint or tinder?
Tim: I... am an enchanter! (As he explodes another tree)
Arthur: By what name are you known?
Tim: There are some who call me... Tim...
Arthur: ...greetings, Tim the Enchanter.

On the UK release of the DVD the actors explain that "Tim" was intended as a particularly unlikely and un-menacing name for such a powerful wizard, but in an interview with Shaun Micallef in 2007, John Cleese claimed that "we chose 'Tim' to annoy Tim Brooke-Taylor."

Whatever the reason, I have a handful of special friends who, as a result of that film, call me The Enchanter.

So, what does this have to do with plumbing, you might rightfully ask? Well, memories of that film got me thinking about Rudolph the Red-nosed Reindeer, and the elf who wanted to be a dentist. For some reason I thought the elf character in Rudolph was also named Tim, but research corrected my memory: He was actually named Hermey — an even more innocuous name than Tim, if ever there was one.
So, the reason I was thinking about Tim and Hermey and dentists was because I recently faced the challenge of designing a dental facility for one of my projects, and it has been an educational adventure.
Dental facilities are a niche of NFPA that is poorly defined, so the design parameters are difficult to embrace. The basic requirements of any dental facility, as anyone who has ever been to the dentist could guess, are compressed air, vacuum and water. For those of us who visit “happy dentists,” there is an element of nitrous oxide involved as well.

Things get a little more complicated when the dental suite is part of a major hospital, which includes dental surgery, as well as the standard dental treatment rooms (DTRs). The typical DTR has DCA (dental compressed air) and DLV (dental low vacuum) provided to the dental chair from the floor below. Often air and vacuum are also provided, on a console behind the dental chair as well for the use of the assistant. Dental chairs also have water, but, since the water must be completely pure, most chairs have a bottle of distilled water mounted to them that is pressurized with the dental air. Take a look next time you go to the dentist. This is done in lieu of relying on a central treated water system that may or may not be of sterile quality.

The dental air provided to the chairs is furnished with the same type of compressors that would provide medical compressed air, except they operate at 95 psi rather than 55 psi. This air is used to power the dental tools and is not intended for respiration, although it is of respiratory quality.

The dental low vacuum is provided by pumps that are somewhat specialized in nature. Most medical equipment vendors do not supply dental vacuum pumps because of their unique requirements; a specialized manufacturer must be sought. Dental low vacuum operates between 6” and 8” Hg, rather than the 15” to 19” Hg of medical vacuum (hence the name dental low vacuum). The system is considered a wet vacuum — piping must slope to the source to allow for drainage. The vacuum pumps must include an amalgam separator as well as a receiving tank that collects the waste water from the system. This separator has a washdown cycle that automatically cleans the tank during off hours.
Major dental suites also include dental surgical treatment rooms and oral surgery rooms. Surgical treatment is similar to a DTR with the addition of a surgical boom that has all the medical gases you would provide in an operating room (i.e. medical air, oxygen, medical vacuum, nitrous oxide, WAGD and nitrogen). Oral surgery has all of these same services, except the dental chair is usually replaced with a surgical table.

Other provisions in a major dental suite are for dental prosthetics, or tooth replacement, and the associated dental prosthetics lab, where the artificial teeth are made. The dental prosthetics room is similar to a DTR, with the addition of fuel gas to fire small ovens for fabricating teeth. The lab also requires fuel gas, for the same reason, on a grander scale, as well as laboratory air at the various technician stations.

Since dental compressed air is not used for respiration, the same air can be used for laboratory purposes, but the piping system should be a dedicated one, with isolation valves at the compressor source to differentiate the two systems.

The dental lab will also include a sterilizer for cleaning the dental tools. Typically, these sterilizers require treated water from the central treated water system, if one is available. Otherwise, a local treatment system should be provided.

Sizing of the dental air and vacuum systems is similar to sizing medical air and vacuum, except the flow rate of the DLV system is greater than its medical vacuum counterpart. Typically, each dental chair should be provided with 7 SCFM of vacuum, with little or no diversity, depending on the size of the system and the nature of the facility. If it is a small facility with one dentist and several chairs, you might be able to apply a diversity, but take care, since the dentist will likely have hygienists who could be using the dental vacuum while the dentist is with another patient. Most of the dental vacuum pump manufacturers have specialized programs for figuring the size of the source equipment.

Dental compressed air is sized based on 3 SCFM per DTR (including dental treatment and oral surgery) with some diversity depending on the number of rooms. To this flow rate, you must add the demand of the lab and sterilizers, if the compressors are serving this need. Flow rates are a function of the kind of equipment served, so some research is required here. A 50% diversity is frequently applied, since the equipment is not used continuously.

Sizing of the other medical gases, when they are required for surgical treatment, oral surgery and recovery, is done much the same as for any hospital. These are all critical areas, so care must be taken to treat them as such, with generous diversities and dedicated zone valve boxes as you would provide for any OR and recovery area.

 

Timothy Allinson is a senior professional engineer with Murray Co., Mechanical Contractors, in Long Beach, Calif. He holds a bsme from Tufts University and an mba from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a leed accredited professional. Allinson is a past-president of aspe, both the New York and Orange County Chapters. He can be reached at laguna_tim@yahoo.com.