A horizontal laminar flow hood is a specialized workstation designed to provide an ultra-clean environment for sensitive work like pharmaceutical compounding, tissue culturing, and electronics assembly. This equipment operates by drawing air through a High-Efficiency Particulate Air (HEPA) filter, which removes 99.97% of airborne particles 0.3 micrometers in size. This process produces a continuous, unidirectional air stream that moves uniformly and horizontally across the work surface, sweeping contaminants away from the product and out of the workspace. Maintaining this controlled environment requires a strict and methodical cleaning protocol to prevent the introduction of contaminants that could compromise the integrity of the work. Regular cleaning is the primary defense against cross-contamination and is necessary to uphold the hood’s function as a primary engineering control.
Essential Preparations and Safety Requirements
Preparing to clean the hood involves a sequence of steps designed to maximize safety and cleaning effectiveness before any physical wiping begins. The first step involves donning the appropriate Personal Protective Equipment (PPE), which must include cleanroom gloves, eye protection, and a dedicated, non-shedding lab coat or gown. Using the correct garb prevents the cleaner’s own particles, such as skin flakes and hair, from introducing contamination into the controlled space.
Gathering the correct supplies is equally important, starting with sterile, lint-free wipes or cloths, which are designed not to shed fibers. The cleaning agents require careful selection, typically involving a dual-step process of cleaning followed by disinfection. A common disinfectant choice is a 70% solution of isopropyl alcohol (IPA) or ethanol, which is effective against many microorganisms and evaporates quickly.
It is important to understand the difference between cleaning and disinfection: cleaning removes visible dirt and organic matter, while disinfection uses a chemical agent to kill nearly all fungi, viruses, and bacteria. Before introducing any cleaning materials, the hood must be shut down by turning off the fan or blower. A waiting period of approximately 30 minutes should follow this shutdown to allow any airborne particulate matter to settle onto the surfaces.
Detailed Cleaning Procedure
The physical cleaning process must adhere to the principle of moving from the cleanest areas to the potentially dirtiest areas to avoid spreading contamination. For a horizontal laminar flow hood, the ceiling is considered the cleanest internal surface, since the HEPA-filtered air originates from the back wall and sweeps across the top. Therefore, the cleaning sequence begins with the interior ceiling, followed by the side walls, and concludes with the work surface or deck.
The most critical aspect of the procedure is the wiping technique, which must be executed using unidirectional, overlapping strokes, never a circular scrubbing motion. Circular motions simply redistribute contaminants across the surface, whereas a linear, overlapping stroke physically moves the particles in a single direction toward the front opening. Each stroke should overlap the previous one by about 25% to 50% to ensure no spot is missed. The wipe should be refolded or replaced frequently to expose a clean surface.
Cleaning agents should never be sprayed directly inside the hood, as the force can damage the sensitive HEPA filter media or electrical components. Instead, the cleaning solution and the disinfectant must be applied by thoroughly wetting the lint-free wipe outside the hood. After the initial cleaning with a detergent or mild cleaner, the disinfectant, such as 70% IPA, must be applied to all surfaces.
The disinfectant requires a specific contact time, or dwell time, as mandated by the manufacturer, to ensure its efficacy in neutralizing microorganisms. This period is typically several minutes, and the surface must remain visibly wet for the entire duration to achieve the stated level of disinfection. Special attention must be paid to the corners, edges, and the grille covering the filter face, wiping gently to avoid damage, but never allowing liquid to pool. Once all surfaces have been cleaned and disinfected, all used wipes and materials must be carefully removed from the hood and disposed of in the appropriate waste container, taking care not to drag them across the newly cleaned surfaces.
Post-Cleaning Steps and Operational Checks
Once the cleaning and disinfection is complete, the immediate next step is to safely remove and dispose of all remaining cleaning materials, including the soiled PPE, from the area. This prevents the introduction of external contaminants back into the newly sanitized environment. The fan or blower for the laminar flow hood can then be switched back on to restart the airflow.
A secondary waiting period, known as the purge time, is required after the fan is reactivated before any sensitive work can begin inside the hood. This time, typically 15 to 30 minutes, allows the HEPA-filtered air to completely sweep the workspace and remove any residual, non-viable particulate matter that may have been aerosolized during the cleaning process. The purge time ensures the interior environment meets its required ISO cleanliness standard before any product is exposed.
For regulatory and quality assurance purposes, the cleaning activity must be logged in a designated record. This documentation should include the date and time the cleaning was performed, the identity of the person who completed the task, and the specific cleaning and disinfecting agents used. This record-keeping establishes a traceable history of the hood’s cleanliness, which is a standard requirement for maintaining compliance in controlled environments.