What control technique could be a source of ignition?

The correct answer is adsorption. This process can create a potential source of ignition under certain circumstances, particularly when it involves materials or chemicals that can generate heat during the adsorption process. Adsorption is when molecules adhere to a surface, potentially concentrating flammable substances. If these substances reach their ignition temperature, they can ignite, resulting in a fire or explosion hazard.

In contrast, filtration and absorption are primarily focused on removing particles or contaminants from a substance without creating significant heat or concentrating ignitable substances. Similarly, evaporation refers to the phase transition from liquid to vapor and may release flammable vapors, but it is not directly a control technique that involves creating ignition sources like adsorption can. Understanding the nature of each technique is vital, particularly in hazardous materials management, to ensure safety and mitigate risks related to ignition sources.