NOTE: Make sure you read the first three posts (in order!) before tackling the rest, or it could be confusing: Post 1 is Designing the future, Post 2 is Setting up the problem, and Post 3 is Estimating basic requirements.


Friday, November 03, 2006

Child Safety Requirements

There are important differences between requirements and specifications. Requirements give specific information about the project (or sub-project) at hand whereas specification give general guidelines to follow. I’ll try to illustrate the distinctions using one of the underdeveloped topics in the Peak Oil Homestead Example Problem: making the Homestead safe for children.

Notice that all ambiguous terms in a requirement must be defined explicitly or by referencing a specification. Also note that not all values are defined in these requirements and specs; there are placeholders that we will fill in with later research.

The Homestead shall have railings (per Spec XYZ) on all exposed stairways.

The Homestead shall provide safety protection for all sharp corners per Spec ABC.

The Homestead shall provide safety barriers (per Spec AAA) around all hazardous areas and devices.

The electrical system shall provide protection for electrical outlets per Spec AAA.

Spec XYZ:
Railings must be X feet high above the stairway. Railings with slats must have a slat spacing of less than Y inches.

Spec ABC:
Corners can be deemed “rounded” or “sharp” by inspection. If pressing your palm on the corner leaves an indent, it requires protection. Protection can consist of foam, sponge, or cloth securely attached to the fixture.

Spec AAA:
A safety barrier near any hot object such as a wood stove or water heater should be at least X feet away and composed of non-flammable materials.
Electrical outlets may be capped with plastic inserts or an external cover.

These specifications are not complete, but hopefully demonstrate what specs should contain.


At 1:55 AM, Anonymous Jeff said...


Love your site, and the systems engineering approach to building sustainable communities. I have a question concerning the use of the term “wood stove”. This seems like it should fall in the realm of design, not requirements where “cooking apparatus” seems like a more appropriate term. There were a number of specific items listed in the specs such as foam, sponge and plastic clips all of which speak to design.

In a pre-peak oil world, these examples seem acceptable because they are materials that are readily available; however when designing for the future, like in a post-peak oil world, little things like this may not be available or desirable. How is this reconciled in the pre-design stage(s)?

Thanks, Jeff

At 6:31 AM, Blogger PeakEngineer said...

You're right that something that specific shouldn't be in the system-level requirements, but in this instance it's actually in the specification. It's saying that in general, this is the type of barrier you should have around a wood stove. The complete specification would list out other important specific cases and the guidelines to be followed.

So, treat the specifications as a separate document (it can actually be from an independent source -- like a building code book) that the requirements refer to.

Acquiring materials and tools post-peak oil does become more difficult, but we haven't outlined anything yet that is prohibitive post-Peak. Each design situation is different (remember that this example problem will likely not represent your situation), and in our assumptions for this problem we declared that the construction would be complete by 2009 (presumably before serious Peak Oil problems arise). If this turns out to be a bad assumption, the design process needs to be re-examined.

Thanks for the comments, Jeff. I'll e-mail you back on your other questions in a couple days -- I'm heading out of town this morning.


At 1:49 PM, Anonymous Jeff said...

Thanks PeakEngineer, I did overlook the criteria that the Homestead Project would be complete in 2009. If there's a rule when creating requirements to leave design out of them, and specs are created simultaneously with requirements, I assumed the same rule would apply to the specs. If that's true, it seems to create a bit of a dilemma if examples are to be given in the specs. I appreciate your insight; this will give me something to mull over. -Jeff

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