Controlled Environments - January/February 2015

Can you provide an overview of how best to keep a cleanroom clean?

“Cleanliness is next to godliness.”

John Wesley, 1778

True story: A colleague once faced the challenge of a sitting Vice President of the United States requesting an opportunity to visit the company’s manufacturing facility – including a tour inside the cleanroom. Management agreed; game on. For more than a week, White House and Secret Service advance teams worked with the company’s facilities, communications, security, and government relations staff, planning the Vice President’s trip down technology lane, in minute detail. All went well until the senior Secret Service contingent arrived, detailing final requirements which included an explosives sniffing dog inspecting the cleanroom just prior to the Vice President’s arrival.

I have no idea what a typical dog hair measures, but we’ve all been taught that a human hair clocks in at 75-100 microns diameter. And we all know that 0.5 micron particles can cause huge problems in a controlled environment. A dog is not a cleanroom’s best friend.

While the Secret Service request may be an extreme example, every facilities engineer faces the responsibility of “keeping the cleanroom clean.” What follows is a high level overview of some basics to keep in play.

Contamination, contamination everywhere

Bomb sniffing canines aside, the world is a dirty place – highly incompatible with clean manufacturing or research requirements whether in life sciences, medical device, electronics, or other specialized manufacturing fields. Fortunately, we humans are much more tolerant of this dirty world where typical office environments hold between 500,000 to 1,000,000 particles measuring 0.5 microns or larger per cubic foot of air.

Pretty ugly in comparison to some common cleanroom classifications and their maximum 0.5 micron contaminant levels: • ISO 03 (Class 1): No more than 1 particle/cubic foot of air;

• ISO 05 (Class 100): No more than 100 particles/cubic foot of air;

• ISO 06 (Class 1,000): No more than 1,000 particles/cubic foot of air;

• ISO 07 (Class 10,000): No more than 10,000 particles/cubic foot of air.

While 0.5 microns is a handy measure for purposes of this article, many industries must control to smaller particles, while also controlling for bacterial and other microbial components.

Contamination is an expensive proposition, causing product lots to be scrapped, research trials to be abandoned, specialized and expensive equipment to fail, and billions of dollars to be lost.

The source of all that “filth”

“If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.” - Sun Tzu, The Art of War

While tradition holds that Sun Tzu, a brilliant Chinese general and strategist whose attributed writings are still influential today, was active in the sixth century BC, he was hardly concerned with cleanroom contamination. But today’s facilities engineer should know both the enemy (sources of contamination) and thyself (in this case, you and your organization’s employees).

I find it handy to broadly classify contamination sources into two broad categories: those emanating from the physical plant, and those from process/human actions. The first includes items like HVAC design; the cleanroom envelop and components such as flooring, wall, and ceiling materials; and tool installation/venting. The second, more variable category includes actions such as maintenance of mechanical systems; cleaning/housekeeping; process controls; selection of support materials such as gowns, gloves, and wipes; and finally (the big variable) – operators. Look at it as the nouns (items) and verbs (actions) of controlled environments.

Addressing the design and engineering considerations of cleanrooms – specifically the selection of floor, ceiling, and wall components; the engineering of an HVAC system within specific humidity, temperature, air velocity, direction, volume, and pressure parameters; and tool installation/venting – could be a separate article. So we’ll skip the “nouns” and focus on the “verbs” that influence keeping the clean in your cleanroom.

Whether particulate matter, film or microbial contamination, or any other contaminant, clean equates to control, and control equates to elimination or minimization. And the most efficient way to eliminate or minimize contamination is at the source.

So, here are the largest source contributors to cleanroom contamination: • Operators and staff;

• Cleaning procedures;

• Maintenance processes;

• Process controls; and • Materials brought into the controlled environment.

It’s not complicated if one engages common sense.

To arms

In the war against contamination, attacking these five enemies is truly a daily battle. But relentlessly targeting the “low hanging fruit” yields victory.

• People: Not unlike business in general, people are the biggest source of contamination in the cleanroom. We’re a walking contamination disaster waiting to happen, spewing skin flakes, hair, body oils, cosmetics, and lint from our clothing. And the faster we move, the more havoc we wreck: it’s widely reported that a person standing or sitting still generates 100,000 0.3 micron particles per minute, while walking at only five mph generates 10,000,000.