What is the impact of an 8-inch deep lintel or 10-inch coffer? It depends.
What if a room (no Fire Marshal Bill allusions unintended) had a 10 ft ceiling? This would suggest a possible (when fire was at the floor) ceiling jet (ceiling jet ~ equal to expanding smoke layer) that is +/- 1 ft deep. This ceiling jet would be impeded by the 10-inch coffer, as the ceiling jet would be impeded by the 8-inch lintel, but there still will be ceiling jet/smoke layer flow under these "obstructions" as soon as the ceiling jet reached it, which was probably *not* the thought the framers had got for this primarily-residential-prescription application. What all that means is... the relative effectiveness of an 8-inch lintel diminishes in-performing-as-an-obstruction (and the logic for using the 8-inch lintel to declare a separate compartment) as the ceiling height increases. So, what is the impact of an 8-inch deep "lintel" in a shower installation to our underlying base question, "*should we include sprinklers in 48 bathrooms that each have 55+/- sq ft area? *The answer is, "the above impact of lintel on a shower is virtually indistinguishable from not having a lintel, for any fire of substance in the shower (i.e. 0.75MW up), but not for reasons of ceiling height, but for reasons of shower area. We are of course ignoring smoldering and small fire conditions (which occur more often than not), but a substantial fire will roll out of the shower and not look back at a typical lintel. To answer the question "*should we include 48 more sprinklers, one each in the bathrooms that are +/- 55 sq. ft?" * I would not try to corrupt the prescription, but take into consideration some more factors that might affect a realistic and reasonable outcome. 1. is there main-compartment-sprinkler that can project significant water spray in through an open bathroom door? 2. is the water supply pressure strong, so that there will be significant overage to the sprinkler mentioned in item #1 ? 3. is the water supply reliable? 4. does the building management team have a solid fire safety record (e.g. Marriott hotels) 5. are there plastic, pressboard or wooden cupboards in the bathroom? or is it just marble, tile and glass? 6. is the shower enclosure ceramic tile, cross-linked thermoset plastic, or worse...thermoplastic? There is no magic to the 55 sq. ft bathroom rule. Bathrooms are no more dangerous at 56 sq. feet than at 54 sq. ft. The framers introduced a go/no-go acceptance criteria to make the decision process easier. But this doesn't guarantee the decision is better. When real life enters the nuanced grey areas that exist near the boundaries of the acceptance criteria...the quick answer provided by a prescriptive acceptance criteria may not always produce the best judgment or most reasonable design. Good judgment can (and should) be applied in making a final decision. If it is any consolation, it is just because we do have these tougher-to-answer questions that we find reasons to justify our incomes. Scot Deal Excelsior Fire/Risk Engineering _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
