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RE: Preventive Maintenance For Lamps
- Subject: RE: Preventive Maintenance For Lamps
- From: "Butner, R Scott" <email@example.com>
- Date: Mon, 30 Aug 2004 10:41:16 -0700
- Cc: "Kennedy, Judith C." <jken461@ECY.WA.GOV>,"Minicucci, Bob" <firstname.lastname@example.org>
- Delivered-To: email@example.com
- Delivered-To: firstname.lastname@example.org
- List-Name: p2tech
- Reply-To: "Butner, R Scott" <email@example.com>
- Thread-Index: AcSOsFdPV3MFlHu1TzS1G3v48DEmCwAABDkwAABAgbA=
- Thread-Topic: Preventive Maintenance For Lamps
some point in time, Judith Kennedy (jken461@ECY.WA.GOV) is alleged to have
said (in part):
anyone provide me with some information on preventive
maintenance programs for commercial/industrial
> where all lamps are periodically changed at the same
they need it or not?
To which I replied:
initially hesitated to post my reply to P2TECH because I don't
have time today to cite enough references. Then I remembered -- "hey,
this is the Internet! It doesn't matter!"
Nonetheless, my understanding (which comes
from preventative maintenance literature in the process industries --
where similar decisions are made about when/how often to replace valve
packings, pump seals, etc) is that over time, an industry (or a company if it is
large enough to have a good sample size) can collect sufficient data regarding
mean time between failure (MTBF) to permit accurate estimation of the lifetime
of a replaceable item. These statistics can also tell you how tightly
clustered the MTBF is around some mean value -- for some types of parts, the
clustering may be very tight (nearly every part fails close to the mean time);
for others, the clustering may be very loose (there is wide variation in the
sobering to note that this table lists the MTBF for the hard disk of the 4-year
old computer which I am writing this on as 10,000 hours. At somewhat over
2,000 hours of compter use per year (you can do the math), perhaps that accounts
for the feeling of impending doom I sometimes feel when I log in for the day?
maybe it's just the evening news that's to blame.
Anyway, the replacement cycle is then pegged to some
percentage (assumedly a number less than 100%) of the MTBF value. What
percentage of this MTBF is used as the trigger for replacement depends on a
number of factors including the standard deviation around that value (how loose
or tight the clustering around that value is), the criticality of the part
(i.e.., the safety issue that Bob refers to), the value of the part relative to
replacement cost, and adjustments for type of service* the part sees.
Obviously, all other things being equal (which they hardly ever are), a high
valued part will be pushed to a greater percentage of it's MTBF than a
low-valued part; a part with a high consequence of failure will be
replaced at a lower percentage of it's MTBF than one which doesn't matter
life example some of us may be (painfully, in my case) familiar with is the
timing belt on your car (or more precisely, my wife's car). Although
the replacement cost of the belt is relatively small (typically under $100 for
the part), the cost of labor is high, so a timing belt will likely
cost $500-700 to replace. Most manufacturers recommend replacement every
60,000 - 70,000 miles.
tell you from personal experience that timing belts will often last 100,000
miles or more.
However, if you push one past it's limit, the result
can be severe engine damage. Really costly severe engine damage.
"Does our insurance cover towing?" kind of engine damage. So it makes
economic sense to replace the timing belt well before its MTBF.
me on this one. :(
I'm drifting off topic again, aren't I? In any event, in the case of lamp
replacement, I suspect that the consequences of single lamp failures are
relatively small; the cost of labor for replacement is high relative to the cost
of the lamp (in most cases). This would especially be true if lamp
replacement were outsourced to a vendor/contractor, so that overheads associated
with the maintenance staff are reduced. In "light" of these factors
(sorry), I would assume that lamps are pushed to a relatively high % of MTBF for
thinking out loud here, but from a p2 perspective, this is a good example of how
our community's focus on p2 as a cost-saving measure (as opposed to an
environmental strategy) is sometimes a bit of a deal with the devil** -- there
are times when p2 objectives (i.e.., extending the lamp utilization to the
maximum possible amount of time) conflict with the economic objectives
(minimizing the total lifecycle cost of providing lighting). Of course,
sometimes this is simply a good indicator that the problem is ripe for
alternative solutions -- daylighting, or perhaps use of LED-based lighting
(since LED's, aside from being more energy efficient, typically have MTBF of
more than 100,000 hours, rather than just a couple thousand).
options notwithstanding, if you're concerned about "premature" lamp replacement,
it might be worth looking at whether there are other locations in the facility
where "replace as needed" lighting can be justified -- and demote the lamps that
are replaced on scheduled replacement to that service when they are
this helps you think constructively about the problem, even if it doesn't answer
all of your questions.
* for example, on traffic lights, the yellow
lamps may be replaced less often since they are on for less time than green or
red due to the nature of the traffic light cycle. So, a logical
policy might be to replace them every OTHER replacement cycle.
Besides, no one pays attention to yellow lights,
before I am taken to task for this statement, I am NOT suggesting that
emphasizing the economic benefits of p2 is not important -- indeed, I suspect
that the realization by the p2 community that this is largely an economic
issue has probably accounted for the bulk of the environmental benefit
brought about via p2. But don't you sometimes find yourself wishing that
protecting the environment was as strong a motivator as saving money.